TM 5-814-8

CHAPTER 6

WASTEWATER TREATMENT PROCESSES

6-1. Preliminary and Primary Waste-water Treatment Processes

a. Introduction. Preliminary treatment ofwastewater generally includes those processesthat remove debris and coarse biodegradablematerial from the waste stream and/or stabilizethe wastewater by equalization or chemical addi-tion. Primary treatment generally refers to asedimentation process ahead of the main systemor secondary treatment. In domestic wastewatertreatment, preliminary and primary processes willremove approximately 25 percent of the organicload and virtually all of the nonorganic solids. Inindustrial waste treatment, preliminary or pri-mary treatment may include flow equalization,pH adjustment or chemical addition that is ex-tremely important to the overall treatment pro-cess. Table 6-1 liss the typical effluent levels bydegree of treatment. This section of the manualwill discuss the various types of preliminary andprimary treatment processes available.

b. Preliminary treatment. An important part ofany wastewater treatment plant is the equipmentand facilities used to remove items such as rags,grit, sticks, other debris, and foreign objects.These interfere with the operation of the facilityand often cause severe problems. Methods of

. removing these materials prior to primary andsubsequent treatment are part of a pretreatmentor preliminary treatment. While a summary dis-cussion of the commonly employed unit opera-tions follows, a more complete description ofdesign criteria which must be used is contained inTM 5-814-3.

(1) Screening and comminution. Screeningand comminution are preliminary treatment pro-cesses utilized to protect mechanical equipment inthe treatment works, to aid downstream treat-ment processes by intercepting unacceptable sol-ids, and to alter the physical form of solids sothey are acceptable for treatment. Screening orcomminution shall always be used for militarydomestic wastewaters.

(a) Screening. Screening devices removematerials which would damage equipment orinterefere with a process or piece of equipment.Screening devices have variedwastewater treatment facilities,are employed as a preliminaryScreens are classified as fine or

applications atbut most oftentreatment step.coarse and then

further classified as manually or mechanicallycleaned. Coarse screens are used in preliminarytreatment, while fine screens are used in lieu ofsedimentation preceding secondary treatment oras a step in advanced wastewater treatment. Finescreens as a preliminary or primary treatment aremore applicable to process or industrial wastes.TM 5-814-3 provides detailed descriptions ofthese units and design considerations.

(b) Comminution. A comminutor acts asboth a cutter and a screen. Its purpose is not toremove but to shred (comminute) the solids.Solids must be accounted for in subsequentsludge handling facilities. Comminutors, like mostscreens, are mounted in a channel and thewastewater flows through them. The rags andother debris are shredded by cutting teeth untilthey can pass through the openings. Some unitsrequire specially shaped channels for proper hy-draulic conditions, resulting in more expensiveconstruction. Treatment. plant design manuals,textbooks, and manufacturer’s bulletins providedetailed information on these units. A bypasschannel is required for all comminutors to permitmaintenance of equipment.

(2) Grit removal. Grit represents the heavierinert matter in wastewater which will not decom-pose in treatment processes. It is identified withmatter having a specific gravity of about 2.65,and design of grit chambers is based on theremoval of all particles of about 0.011 inch orlarger (65 mesh). For some sludge handling pro-cesses, it may be necessary to remove, as aminimum, grit of 0.007 inch or larger (100 mesh).Grit removal, compared to other unit treatmentprocesses, is quite economical and employed toachieve the following results:

–Prevent excessive abrasive wear of equip-ment such as pumps and sludge scrapers.

–Prevent deposition and subsequent oper-ating problems in channels, pipes, andbasins.

–Prevent reduction of capacity in sludgehandling facilities.

Grit removal facilities shall be used for combinedsewer systems or separate sanitary systemswhich may have excessive inert material. Gritremoval equipment should be located after barscreens and comminutors and ahead of raw sew-age pumps. Sometimes it is not practical to locate

6-1

Table 6-1. Typical effluent levels of principal domestic wastewater characteristicsby degree of treatment (mg/L unless noted otherwise)

Wastewater Treatment .Average Advanceda

Raw (1) (2) 3 (4) ( 5 ) —Parameter Wastewater Primary Secondary (l)+(2)+NRb (3)+PRC (4)+SSORd

BOD 300 195 30e 15 5 1

COD 600 400 150 100 45 12

Suspended Solids 300 120 30e 20 10 1

Amnonia (as N) 25 25 28 3 3 3

Phosphate (as P) 20 18 14 13 2 1

pH (units) 7 6-9 6-9e 6-9 6-9 6-9

Fecal Coliform 1,000,000 15,000 200e 200 200 100(no. /100 mL)

aReasonable levels but not necessarily minimum for all constituents.bNR = Nitrogen Removal or ConversionCPR = Phosphorus RemovaldSSOR = Suspended Solids and Organics RemovaleEnvironmental Protection Agency, Secondary Treatment Information, 40 CFR, Part 133, FederalRegister, Monday, 30 April 1973.

TM 5-814-8

the grit removal system ahead of the raw sewagepumps because of the depth of the influent line.Therefore, it may be required to pump thewastewater containing grit. If this mode is se-lected, pumps capable of handling grit should beemployed.

(a) Horizontal flow grit chambers. Thistype of grit chamber is designed to allowwastewater to pass through channels or tanks ata horizontal velocity of about one foot per second.This velocity will allow grit to settle in thechannel or tank bottom, while keeping the lighterorganic solids in suspension. Velocity control andother design features are covered in TM 5-814-3.

(b) Detritus tanks. A grit chamber can bedesigned with a lower velocity to allow organicmatter to settle with the grit. This grit-organicmatter mixture is referred to as detritus and theremoval devices are known as detritus tanks.When detritus tanks are employed, the organicmatter is separated from the grit by either gentleaeration or washing the removal detritus tore-suspend the organic matter. Several propri-etary systems are available to accomplish this,and the advantage over other types is that theconfiguration of the tank is simple and thesystem allows for continuous removal of grit.

(c) Aerated grit chambers. As the nameimplies, diffused air can be used to separate gritfrom other matter. A secondary benefit to theaeration method is that is also freshens thewastewater prior to further treatment; quite oftenit is used in conjunction with a preaerationfacility. The different types of grit removal facili-ties employed are described in TM 5-814-3.

(3) Preaeration. Methods of introducing sup-plemental oxygen to the raw wastewater aresometimes used in preliminary treatment. Thisprocess is known as preaeration and the objec-tives are to:

—Improve wastewater treatability.—Provide grease separation, odor control,

and flocculation.—Promote uniform distribution of sus-

pended and floating solids to treatmentunits.

—Increase BOD removals in primary sedi-mentation.

This is generally provided by either separateaeration or increased detention time in an aeratedgrit chamber. Provisions for grit removal areprovided in only the first portion of the tank(125).

(4) Equalization. Equalization has limited ap-plication for domestic wastes, but should beemployed for many industrial discharges includ-

ing some of those from military industrial manu-facturing processes as discussed later in thischapter. Equalization reduces fluctuations of theinfluent to levels compatible with subsequentbiological or physical-chemical processes. A prop-erly designed facility dampens the wide swings offlow, pH, BOD, and other parameters to levelssuch that downstream systems operate moreefficiently and economically, and can be con-structed at a reduced capital investment. Properequalization will also minimize system upsets andmore consistently provide a better quality efflu-ent. A graphical example of how an equalizationfacility can stabilize a wastewater having signifi-cant cyclic pH variations is illustrated in figure6-1. While there are definite primary benefits forequalization, a facility can also be designed toyield secondary benefits by taking advantage ofphysical, chemical, and biological reactions whichmight occur during retention in the equalizationbasin. For example, supplemental means of aera-tion are often employed with an equalizationbasin to provide:

—Better mixing.—Chemical oxidation of reduced com-

pounds.—Some degree of biological oxidation.—Agitation to prevent suspended solids

from settling.If aeration is not provided, baffles or mechanicalmixers must be provided to avoid stratificationand short circuiting in equalization basins. Thesize and shape of an equalization facility will varywith the quantity of waste and the patterns ofwaste discharge. Basins should be designed toprovide adequate capacity to accommodate thetotal volume of periodic variation from thewastewater source (125) (130).

(5) pH control. Similarly to equalization, theuse of pH control as a preliminary treatment stepis usually limited to treatment of industrialprocess wastes. It is necessary to regulate pHsince treatment processes can be harmed byexcessively acidic or basic wastes. Regulation ofthis parameter may be necessary to meet effluentlevels specified for secondary treatment. Controlof the pH at elevated levels is usually required toprecipitate certain heavy metals and/or alleviatean odor producing potential.

(6) Flotation. In preliminary treatment, flota-tion is sometimes used for wastes which haveheavy loads of grease and finely divided sus-pended solids. These are mainly systems havinglarge industrial discharges and may apply tomilitary installations with significant oil andgrease quantities from manufacturing or laundry

6 - 3

TM 5-814-8

10

8

4

2

operations.

INFLUENT TO PLANT

.

EFFLUENT FROMEQUALIZATION

TIME

Figure 6-1. The effect of equalization on a wastewater with variable pH.

Domestic waste may also containlarge quantities of grease from food preparation.Use of air to float materials may relieve scumhandling in a sedimentation tank and lower thegrease load to subsequent treatment units. Gritremoval is often incorporated with a flotation unitproviding sludge-removal equipment. Flotation de-sign guidelines are available, but bench testing isdesirable to finalize the criteria and expectedperformance.

(7) Other methods. Other preliminary treat-ment steps include coagulation and chlorination.Coagulation is a part of sedimentation as pre-sented later in this chapter. Chlorine additionsare often made to the plant influent for odorcontrol (120). Two other operations which usuallyprecede any treatment process include pumpingand flow measurement. Wastewater bypassesmust also be provided.

(a) Pumping. Pumping facilities may beemployed to gain sufficient head for thewastewater to flow through the treatment worksto the point of final disposal. Pumping is alsogenerally required for recirculation of all or partof the flow around certain units within the plant.Pumping facilities are classified as influent, efflu-ent, or recirculation stations and perform a criti-cal function. Provisions shall be made for reliabil-ity to ensure the facility is operable at all times.This means the largest pump has a standbyduplicate so that pumping capacity is available tomeet peak flows. It also means duplicate sourcesof power and/or standby power must be provided.

6 - 4

U.S. EPA requires this flexibility for municipalfacilities. Guidelines for pumping facilities areavailable in TM 5–814-3.

(b) Flow Measurement. Metering and in-strumentation devices in numerous sections of awastewater treatment facility are necessary foradequate plant control and operating flexibility.Proper monitoring of effluent characteristics isrequired to comply with NPDES permits. Use ofdevices such as Venturi meters, weirs, andParshall flumes predominate. Parshall flumes arethe preferred flow measuring method for militaryinstallations. TM 5-814-3 provides a descriptionof sizing and design considerations. The need forother meters and instrumentation throughout thetreatment facility will be dictated by the size ofthe facility, complexity, and need for record-keeping and operator control of the process. Insmall installations, where maintenance and avail-ability of spare parts may be difficult, meteringcan be a problem. Reference should be made topublications (120) for guidelines on types ofmeasurement systems available, limitations, andpreliminary design criteria. Also standard text-books and literature from equipment manufactur-ers should be investigated thoroughly prior toselection of type and degree of plant measure-ment and instrumentation.

(c) Wastewater bypasses. Piping arrange-ments and duplicate treatment units may beprovided to the maximum practical extent so thatan inoperative unit, such as a clarifier, may bebypassed without reducing the overall treatment

TM 5-814-8

efficiency of the plant. Bypassing of the entirewastewater treatment plant through an emer-gency overflow structure during periods of ex-traordinarily high flow must be provided. In allcases, this diverted flow shall be disinfected andscreened, and the quantity of flow measured andrecorded. The appropriate regulatory agency shallbe notified of every bypass occurrence. When thewastewater is discharged to a waterway whichcould be permanently or unacceptably damagedby the quantity of bypassed wastewater, such asshellfish waters, drinking water reservoirs, orareas used for water contact sports, provisionshall be made to intercept the bypassed flow in aholding basin. The intercepted flow shall then berouted back through the treatment facility assoon as possible. Bypasses for diversion of flowaround treatment plants will be locked in a closedposition. The bypass must be controlled by super-visory personnel.

c. Primary treatment. Primary treatment forthe purposes of this manual will be limited tosedimentation with and without chemical addi-tion. Other unit processes are usually combinedwith sedimentation as a part of “primary treat-ment”, including some degree of preliminarytreatment, sludge treatment and disposal, andchlorination as a disinfection step. For manyyears, water quality criteria specified only the useof primary treatment for domestic wastewaters.Primary treatment is no longer acceptable as thetotal wastewater treatment step prior to dis-charge to a receiving body of water and second-ary treatment must now be employed to meetregulatory criteria. Therefore, the discussion pre-sented herein on primary treatment shall beutilized by military personnel concerned with:

—Alternatives that must be considered forexisting treatment facilities which are to beupgraded to meet effluent limitations andwater quality criteria.

—Design factors and alternatives that mustbe considered when planning a newwastewater treatment facility.

(1) Plain sedimentation. Wastewater, afterpreliminary treatment, undergoes sedimentationby gravity in a basin or tank sized to producenear quiescent conditions. In this facility, settle-able solids and most suspended solids settle tothe bottom of the basin. Mechanical collectorsshould be provided to continuously sweep thesludge to a sump where it is removed for furthertreatment and disposal. Skimming equipmentshould be provided to remove those floatablesubstances such as scum, oils, and greases whichaccumulate at the liquid surface. These skim-

mings are combined with sludge for disposal.Removals from domestic wastewaters undergoingplain sedimentation will range from about 30 to40 percent for BOD and in the range of 40 to 70percent for suspended solids. With optimum de-sign conditions for sedimentation, BOD and sus-pended solids removal efficiency is dependentupon wastewater characteristics and the propor-tion of organics present in the solids. One of themost important design parameters if the overflowrate, usually expressed in gal/day/sq ft, which isequal to the flow in gal/day divided by thesettling surface area of the basin in square feet.Usually average daily flow rates are used forsizing facilities. The flow rates, detention time,and other factors which shall be employed fordesign purposes are documented in TM 5-814-3.

(a) Secondary treatment sedimentation fa-cilities. It should be recognized that design princi-ples of secondary sedimentation tanks are signifi-cantly different than those for primary tanks, thefundamental difference being in the amount andnature of solids to be removed. Primary sedimen-tation facilities are basically designed on overflowrate alone; secondary units must be designed forsolids loading as well as overflow rate. Referenceshould be made to TM 5–8 14–3 for designcriteria.

(b) High-rate settlers. In recent years, thedevelopment of high-rate settlers has provenquite promising for both primary and secondarysedimentation applications. These have been usedprimarily to improve performance and to increasetreatment capacity of existing plants and shouldreceive attention for upgrading military facilities.The theory is that sedimentation basin perfor-mance can be improved by introducing a numberof trays or tubes in existing facilities, sinceefficiency is independent of depth and detentiontime. Until recent years, use of trays or tubeswas unsuitable on a practical basis because ofdifficult sludge collection and removal. Theseproblems have been largely overcome althoughslime growths may cause flow restrictions andrequire periodic cleaning. The principal advantageof the settlers is their compactness which reducesmaterial costs and land requirements. For mostmilitary installations, the land savings is notcritical but cost reductions will be important.Settlers do not improve the efficiency of primarysedimentation facilities that are already achievingreasonably high removals of suspended solids.Available data indicate that where the settlershave been installed in existing units, it has beenpossible to increase the surface overflow rate ofboth primary and final sedimentation systems

6 - 5

TM 5-814-8

from 2 to 5 times the conventional rate while stillmaintaining about the same suspended solidseffluent level. Manufacturer’s bulletins and U.S.EPA Technology Transfer series documents pro-vide data on design criteria.

(2) Sedimentation with chemical coagulation.Sedimentation using chemical coagulation hasbeen implied mainly to pretreatment of industrialor process wastewaters and removal of phospho-rus from domestic wastewaters. Chemical usageas a pretreatment step for industrial wastes andphosphorus removal is discussed later. The use ofchemical coagulating agents to enhance the re-moval of BOD and suspended solids has not beenused extensively on domestic wastewaters, sinceit is not usually economical or operationallydesirable. However, special applications may existat some installations. Advantages of increasedsolids separation in primary sedimentation facili-ties are:

–A decrease in organic loading to second-ary treatment process units.

–A decrease in quantity of secondarysludge produced.

–An increase in quantity of primary sludgeproduced which can be thickened anddewatered more readily than secondarysludge.

Chemicals commonly used, either singularly or incombination, are the salts of iron and aluminum,lime, and synthetic organic polyelectrolytes. It isdesirable to run jar studies to determine theoptimal chemicals and dosage levels. The use of agiven chemical(s) and effluent quality must becarefully balanced against the amount of addi-tional sludge produced in the sedimentation facil-ity. Design information and guidance is containedin the U.S. EPA Technology Transfer seriesdocuments.

(3) Other methods. For some industrialwastes which contain large amounts of floatableand finely suspended matter, flotation may beused in lieu of sedimentation as a cost-effectivemeans of primary treatment. Some wastewatertreatment alternatives, including ponds and ex-tended aeration, do not require primary treatmentas a distinct process step. Other secondary treat-ment processes could operate without primarytreatment but it is cost-effective to remove thesuspended organics physically rather than biologi-cally.

6 - 2 . B i o l o g i c a l W a s t e w a t e r T r e a t m e n tProcesses

a. Introduction. Biological treatment processesare those that use microorganisms to coagulate

and remove the nonsettleable colloidal solids andto stabilize the organic matter. There are manyalternative systems in use and each uses biologi-cal activity in different manners to accomplish treatment. Biological processes are classified bythe oxygen dependence of the primary microor-ganism responsible for waste treatment (125). Inaerobic processes, waste is stabilized by aerobicand facultative microorganisms; in anaerobic pro-cesses, anaerobic and facultative microorganismsare present. The discussion of biological treat-ment processes has been further divided into thefollowing two categories:

—Suspended growth processes.—Fixed growth processes.(1) Suspended growth processes refer to

treatment systems where microorganisms andwastewaters are contained in a reactor. Oxygen isintroduced to the reactor allowing the bilogicalactivity to take place. Examples of suspendedgrowth processes include ponds, lagoons andactivated sludge systems.

(2) Fixed growth processes refer to systemswhere a biological mass is allowed to grow on amedium. Wastewater is sprayed on the mediumor put into contact in other manners. The biologi-cal mass stabilizes the wastewater as it passesover it. Examples of fixed growth processesinclude trickling filters and rotating biologicalcontractors.

b. Suspended growth processes.(1) Ponds. Ponds have found wide-spread us-

age in the U.S. In 1968, 34.7 percent of thenearly 10,000 secondary treatment systems oper-ating in the U.S. were in the category of stabiliza-tion ponds (49). Waste treatment ponds can bedivided into three general classifications: aerobicponds, aerobic-anaerobic (facultative) ponds, andanaerobic ponds. Ponds are sized on an averageBOD loading or detention time basis and arequite sensitive to climate and seasonal variations.

(a) Aerobic ponds. Photosynthetic pondsare 6 to 18 inches deep with BOD loadingsranging from 100 to 200 lb per acre per day anddetention times of 2 to 6 days. These are usuallymixed intermittently, generally by mechanicalmeans, to maximize light penetration and algaeproduction. A very high percent of the originalinfluent BOD is removed, but due to algaegrowth and release to the effluent, overall remov-als are in the 80 to 95 percent range. Suspendedsolids in the effluent are also mainly due to algae.Lower efficiencies occur during warmer periods ofthe year due to algal growths, and during ex-tremely cold periods due to decreased biologicalactivity and freezing. Aerated aerobic ponds uti-

6 - 6

TM 5-814-8

lize oxygen mixed with the wastewater eitherfrom diffused air or mechanical means, withphotosynthetic oxygen generation not playing amajor role in the process. These ponds are 6 to 20feet deep with BOD loadings ranging from 100 to300 lb per acre per day and detention times of 2to 7 days. BOD and suspended solids removals inthe range of 80 to 95 percent are obtained if aquiescent cell is provided to effect solids removalafter aeration. Aerated aerobic ponds may beconsidered for military applications where flow isvariable or land is precious. Without the aeratorsoperating, the system might function as anaerobic-anaerobic (facultative) pond during lowloads.

(b) Aerobic-anaerobic (facultative) ponds.These ponds consist of three zones: a surfacezone of algae and aerobic bacteria in a symbioticassociation; an intermediate zone populated withfacultative bacteria (aerobic or anaerobic); and ananaerobic bottom zone where settled organic sol-ids are decomposed by anaerobic bacteria. Theponds, operated in natural aeration mode, are 3 to8 feet deep with BOD loadings ranging from 10to 100 lb per acre per day and detention time of10 days to 1 year. BOD removals of 80 to 95percent are obtained with proper operation andloadings, but suspended solids removals varybecause of algal carryover. These ponds may alsobe partially mixed using mechanical or diffusedaerators to supply some oxygen. Mechanicallymixed ponds normally have BOD loadings rang-ing from 30 to 100 lb per acre per day; detentiontimes of 7 to 20 days; operational depths of 3 to8 feet; and, BOD removals of 90 to 95 percent.

(c) Anaerobic ponds. These ponds haveBOD loadings in the range of 10 to 700 lb peracre per day and can provide removals of 50 to 80percent. Detention times range from 30 days to 6months and operational depths range from 8 to15 feet. Anaerobic ponds have been used princi-pally in industrial waste applications and particu-larly in meat packing wastes. Due to the natureof the pond environment, these treatment unitsgenerally produce severely offensive odors. Theyare normally not used by themselves and in orderto produce a higher quality effluent, must befollowed by an aerobic pond. Anaerobic pondsshould not be utilized for military wastewatersexcept under special circumstances.

(d) Other considerations. In treatment ofprincipally domestic wastes, there are additionalfactors to consider (44)(154). Aside from notmeeting effluent criteria, operating problems in-clude odors, colored effluent, high effluent sus-pended solids, mosquito and insect problems and

weeds. A study (154) indicated that of 21 differ-ent pond installations studied, none would consis-tently meet the secondary treatment effluentrequirement of 30 mg/L BOD. Similarly, of 15installations reporting effluent suspended solidsvalues, none would consistently meet the 30 mg/Leffluent limit. New wastewater treatment ponddesigns and existing installations being upgradedmust recognize and provide methods which willachieve required effluent levels. Definitive designcriteria for all situations are beyond the scope ofthis manual. EPA Technology Transfer seriesdocuments and similar publications should beconsulted when planning a new wastewater treat-ment pond facility or when assessing alternativesfor upgrading an existing pond system. Locallyapplicable design criteria considering the effect ofclimate should be used when planning new orupgrading existing facilities. Wide variations incriteria are followed in the U.S. in terms ofloading rates, detention times, depths and num-ber of cells required. While most States in themidwest relate to a BOD design loading criteriain pounds BOD per acre per day, the principaldesign factor in northern states is retention time,primarily because of the extreme winter tempera-tures. In terms of organic loading, pounds ofBOD per acre per day, State design criteria rangefrom less than 20 in the northern states to ashigh as 75 in the southern, southwestern orwestern states, reflecting temperature effects onperformance.

(2) Activated sludge. Activated sludge is anefficient process capable of meeting secondarytreatment effluent limits. In recent years, thisprocess has undergone significant changes andimprovements from the conventional activatedsludge process. For further information on theprocess itself or its modifications, referenceshould be made to TM 5-814-3. The principalfactors which control the design and operation ofactivated sludge processes are:

—Detention time.—BOD volumetric loading.—Food to microorganism (F/M) ratio.—Sludge age or solids retention time (SRT).

While all of these parameters have been used tosize facilities, the most commonly used are theF/M ratio and the SRT. Reference should be madeto textbooks or TM 5-814-3 for further explana-tion and limitations to be considered when deal-ing with these parameters. Secondary sedimenta-tion is particularly important for activated sludgesystems. The design of these units is based onoverflow rate and solids loading. Design criteriafor various size plants and process modifications

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TM 5-814-8

are available (152). A number of variations of theconventional activated sludge process were devel-oped to achieve greater treatabilit y, to minimizecapital andlor operating costs or to correct aproblem. While not all of the variations arementioned herein, the following should be evalu-ated when considering a new facility, or upgrad-ing an existing primary or secondary facility:

–Completely-mixed.—Step aeration.—Contact stabilization.—Extended aeration.—Pure oxygen system.

Summary characteristics on design criteria, re-moval efficiencies and basic applications of themodifications are described in table 6-2. Based onthe overall BOD removal efficiency reported,most variations are able to achieve a high degreeof treatment. The extended aeration system is aflexible system, but is more cost-effective forsmall populations. Extended aeration and contactstabilization are most applicable as packageplants and are described under that heading.Activated sludge systems are commonly designedto accomplish two or more of the operating modesto accommodate flexible operational requirements.An example is the completely-mixed and stepaeration systems. From the data in table 6-2, itcan be seen that depending upon volumetricloading, F/M or detention time, selection of onevariation over another can result in significantdifferences in the size of the aeration basins. Theinformation presented in table 6-2 covers therange which has been experienced.

(a) Conventional. The conventional acti-vated sludge process employs long rectangularaeration tanks which approximate plug-flow al-though some longitudinal mixing occurs. Thisprocess is primarily employed for the treatmentof domestic wastewater. Return sludge is mixedwith the wastewater prior to discharge into theaeration tank. The mixed liquor flows through theaeration tank during which removal of organicsoccurs. The oxygen utilization rate is high at theentrance to the tank and decreases toward thedischarge end. The oxygen utilization rate willapproach the endogenous level toward the end ofthe tank. Principle disadvantages of conventionalactivated sludge treatment in industrial applica-tion are:

—The oxygen utilization rate varies withtank length and requires irregular spac-ing of the aeration equipment or amodulated air supply.

—Load variation may have a deleteriouseffect on the activated sludge when it

is mixed at the head end of the aera-tion tanks.

—The sludge is susceptible to slugs or spills of acidic, caustic or toxic materi-als.

(b) Completely mixed. In the completelymixed process, influent wastewater and recycledsludge are introduced uniformly throughout theaeration tank. This flow distribution results in auniform oxygen demand throughout the aerationtank which adds some operational stability. Thisprocess may be loaded to levels comparable tothose of the step aeration and contact stabiliza-tion processes with only slight reductions com-pared to the removal efficiencies of those pro-cesses. The reduced efficiency occurs becausethere is a small amount of short circuiting in thecompletely mixed aeration tank.

(c) Step aeration. The step aeration processis a modification of the conventional activatedsludge process in which influent wastewater isintroduced at several points in the aeration tankto equalize the F/M, thus lowering the peakoxygen demand. The typical step aeration systemwould have return activated sludge entering thetank at the head end. A portion of the influentalso enters near the front. The influent piping isarranged so that an increment of wastewater isintroduced into the aeration tank at locations down the length of the basin. Flexibilityof opera-tion is one of the important features of thissystem (125). In addition, the multiple-point intro-duction of wastewater maintains an activatedsludge with high absorptive properties. This al-lows the soluble organics to be removed within ashorter period of time. Higher BOD loadings aretherefore possible per 1000 cu ft of aeration tankvolume.

(d) Contact stabilization. The contact stabi-lization process is applicable to wastewaters con-taining a high proportion of the BOD in sus-pended or colloidal form. Since bio-adsorption andflocculation of colloids and suspended solids occurvery rapidly, only short retention periods (15-30minutes) are generally required. After the contactperiod the activated sludge is separated in aclarifier. A sludge reaeration or stabilization pe-riod is required to stabilize the organics removedin the contact tank. The retention period in thestabilization tank is dependent on the time re-quired to assimilate the soluble and colloidalmaterial removed from the wastewater in thecontact tank. Effective removal in the contactperiod requires s u f f i c i e n t a c t i v a t e d s l u d g e t o remove the colloidal and suspended matter and aportion of the soluble organics. The retention

Table 6-2. Summary characteristics of the activated sludge process variations

Food/Micro- Overal1organism Mixed Liquor BOD

Volume Loading Ratio (F/M) Suspended RemovalProcess lb BOD/1,000 lb BOD/lb Solids (MLSS) Detention Efficiency,

Variation cu ft/day MLVSS/day mg/L Time, hr percent Comments

Conventional(plug flow)

Completely-Mixed

Step Aeration

ContactStabilization

Extended Aeration

Pure OxygenSystem

aContact Unit.

20-40

50-120

50-60

60-75

10-25

100-250

b

Stabilization unit.

0.2-0.5 1,000-3,000

0.2-0.6 3,000-6,000

0.2-0.4 2,000-3,500

0.2-0.6 1,000-3,000;4,000-8,000

0.05-0.2 3,000-6,000

0.3-1.0 4,000-8,000

4-8

3-6

3-6

0.2-l.5a

3-6b

18-36

1-10

85-95

85-95

85-95

80-90

75-90

85-95

TM 5-814-8

time in the stabilization tank must be sufficientto stabilize these organics. If it is insufficient,unoxidized organics are carried back to the con-tact tank and the removal efficiency is decreased.If the stabilization period is too long, the sludgeundergoes excessive auto-oxidation and losessome of its initial high removal capacity. Increas-ing retention period in the contact tanks increasesthe amount of soluble organics removed anddecreases required stabilization time.

(e) Extended aeration. The extended aera-tion process operates in the endogenous respira-tion phase of the growth curve, which necessi-tates a relatively low organic loading and longaeration time. Thus it is generally applicable onlyto small treatment plants of less than 1 mgdcapacity (125). This process is used extensivelyfor prefabricated package plants. Although sepa-rate sludge wasting generally is not provided, itmay be added where the discharge of the excesssolids is objectionable.

(f) Pure oxygen system. The variations setforth in table 6-2, with the exception of the pureoxygen system, represent flow models which arebased on plug flow or completely mixed systems.Some systems use a diffused air system, othersare more applicable to mechanical aeration, andsome variations are adaptable to either aerationsystem. All of the systems, with the exception ofthe pure oxygen system, use air as the source ofoxygen. The principal distinguishing features ofthe pure oxygen system are that it utilizeshigh-purity oxygen as a source of oxygen andemploys a covered, staged aeration basin for thecontact of the gas and mixed liquor (49). To date,the system has demonstrated its greatest applica-bility and cost-effectiveness for treatment of highstrength industrial wastes and for large plantstreating domestic wastes. Thus, pure oxygensystems for military wastewaters have limitedapplication.

(g) Continuous loop reactors. The continu-ous loop reactor (CLR) is best described as anextended aeration activated sludge process. Theprocess uses a continuously recirculating closedloop channel(s) as an aeration basin. The reactoris sized based upon the wastewater influent andeffluent characteristics with emphasis given tothe hydraulic considerations imposed by the basingeometry. hydraulic detention times range from10 to 30 hours and the mixed liquor concentrationin the basin is typically 4,000 to 5,000 mg/L. Toprovide the necessary oxygen to the system andimpart a horizontal velocity, several pieces ofequipment are available. These include:

—Brush aerators.

—Low speed surface aerator as used inthe Carrousel system.

—Jet aeration.—Diffused aeration with slow speed mix-

ers.Clarification can be accomplished using a conven-tional clarifier or by using an integral clarifier aswith the Burns and McDonnell system (159).Advantages of the CLR process include:

–The ability for the system to handleupset loading conditions.

–Produces low sludge quantities.–Can provide for vitrification and

denitrification.–Typically produces very good and sta-

ble effluent characteristics.–Simplicity of operation.

The major disadvantages include the potentialwashout of the system by excessive hydraulicflows and the large land area and basin sizes thatare required due to the typically high detentiontimes.

(h) Nitrification. The kinetics and designcriteria for this system are already well defined.Two important considerations are maintenance ofa proper pH and temperature. Nitrification is avery temperature-sensitive system and the effi-ciency is significantly suppressed as the tempera-ture decreases. For example, the rate of vitrifica-tion at pH of 8.5 and 50 degrees F is only about25 percent of the rate at 86 degrees F. Treatmentfacilities located in northern climates must besized at the appropriate loading rate to accom-plish the desired effluent level if required toprovide year-round vitrification. The loading ratesignificantly affects the capital costs for construc-tion of the nitrification tanks. The optimum pHhas been determined to range between 8.4 and8.6. However, for those wastewaters where itwould be necessary to provide chemical-feedingfacilities for pH adjustment, the cost-effectivealternative may be to provide additional tankageto allow for the reduced biological activity whenthe pH is not optimum.

(i) Biological denitrification. As with nitrifi-cation, denitrification is a process which involvesfurther removal of the nitrogen by conversion ofthe nitrate to nitrogen gas. This represents aprocess for the ultimate removal of nitrogen fromwastewater. As with vitrification, there are anumber of system configurations that have beendeveloped for denitrification. The most promisingsystem alternatives include suspended growthand columnar systems (46). While there are ad-vantages and disadvantages to either alternative,the more feasible system for military installations

6-10

TM 5-814-8

will depend somewhat on effluent criteria. Wheresuspended solids are critical, a columnar unit mayalso serve as a filter. In other instances, the

. suspended growth system will usually be mostappropriate.

c. Fixed film processes.(1) Trickling filters. This type of treatment

method has proven very popular over numerousyears in the U.S. In 1968, more than 3,700trickling filter installations existed in this coun-try. In the past, the use of the trickling filter hasbeen considered as the ideal method for popula-tions of 2,500 to 10,000. The principal reasons forits past popularity have been cost, economics andoperational simplicity as compared to the acti-vated sludge process.

(a) Types. The trickling filter process iswell documented in TM 5-814-3 and will not berepeated herein. The types of trickling filters usedand their basic design criteria are set forth intable 6-3. BOD and hydraulic loadings are basedon average influent values. Filters at militaryinstallations have either been low or high ratesingle stage facilities. One advantage of most lowrate filters is that the longer solids retention time(SRT) in the unit allows for production of ahighly nitrified effluent, provided the climaticconditions are favorable. By comparison, interme-diate and high rate filters, which are loaded athigher organic and hydraulic loadings, do notachieve as good an overall BOD removal effi-ciency and preclude the development of vitrifyingbacteria. The other classification of filters arethose termed as super rate. These employ syn-thetic media and have been shown to be able tosustain much higher loadings than a stone me-dium unit. As a result, the super rate filters, inaddition to normal applications for domestic andindustrial wastewaters, have found applicationsas roughing filters prior to subsequent treatmentfacilities. The large surface area per unit volume(specific surface area) and high percent voids ofsynthetic media allow higher organic and hydrau-lic loadings. The greater surface area permits alarger mass of biological slimes per unit volume.The increased void space allows for higher hy-draulic loadings and enhanced oxygen transferdue to increased air flow.

(b) Performance. Most existing trickling fil-ter installations must be upgraded to meet thenew secondary treatment requirements. Decreas-ing hydraulic or organic loading at existing facili-ties will not produce a significant increase inBOD removal above original design values; in-stead, additional treatment operations will beneeded to achieve greater BOD removals. Perfor-

mance of trickling filters is dependent uponseveral other factors including: wastewater char-acteristics, filter depth, recirculation, hydraulicand organic loading, ventilation and temperature.While all of these factors are important,wastewater temperature is the one which is mostresponsible for secondary effluent criteria notbeing met during winter operating conditions.Based on data from several high rate filters inMichigan, filter performance was observed tovary 21 percent between summer and wintermonths. Covering trickling filters or providing anadditional stage should be considered for improv-ing and maintaining performance.

(2) Rotating biological contractors. Anothertype of biological secondary treatment system isthe rotating biological contactor. This system hasbeen used in Europe, particularly West Germany,France and Switzerland. Manufacturers indicate1000 installations in Europe treat wastewatersranging in size from single residences to 100,000population equivalent. Domestic, industrial andmixtures of domestic and industrial wastewatershave been treated. In the process, the largediameter corrugated plastic discs are mounted ona horizontal shaft and placed in a tank. Themedium is slowly rotated with about 40 percentof the surface area always submerged in theflowing wastewater. The process is similar infunction to trickling filters since both operate asfixed film biological reactors. One difference isthat the biomass is passed through thewastewater in the biological contactor systemrather than the wastewater over the biomass asin a trickling filter unit. No sludge or effluentrecycle is employed. The system has severaladvantages, including:

–Low energy requirements compared withactivated sludge.

–Small land area requirement comparedwith trickling filters.

–A high degree of vitrification can beachieved.

—A more constant efficiency can beachieved during cold weather than withtrickling filters since the units are easilycovered. The covers allow sufficient venti-lation, but minimize the effect of lowambient air temperatures.

While the system has achieved high BOD re-moval efficiencies on domestic wastewaters in theU. S., pilot testing should be performed for anyindustrial application. A recent U.S. EPA study(42) on an industrial waste showed the biologicalcontractors could not perform at the anticipatedloading rate and achieve required removal efficien-

Table 6-3. General trickling filter design criteria

Organic Loadinglb BOD/1000 cu ft/day Depth, ft

TM 5-814-3 Hydraulic T M-5-814-3Design Loading Design

Filter Type Literature Criteria mgad Literature Criteria

Low Rate 10-20 up to 14 2-4 5-7 6(Standard )

Intermediate 15-30 -- 4-10 -- --

High Rate

Super Rate(Synthetic

up to 90 up to 70 10-30 3-6 3-6

- - - - Less Than 50Media)

-- --

TM 5-814-8

ties. It also demonstrated that the activatedsludge process was better able to handle shockloads. Although the system may not be applicablefor certain industrial waste applications unlesspretreatment is provided, it should be consideredfor upgrading existing military treatment plantstreating primarily domestic wastewater. The pro-cess has potential as a second stage unit withexisting trickling filters to improve performanceand also as a vitrification unit. The rotatingbiological contractor can be considered as anoption, however, the use may be limited to add-onor advanced wastewater treatment capacity fornitrogen removal until the RBC equipment reli-ability and economics have been improved.

(3) Activated biological filter. An activatedbiofilter (ABF) is a tower of packed redwood orother media which supports the growth of at-tached microorganisms. Influent wastewater ismixed with recycled solids from the clarifier andreturned mixed liquor. The mixture is sprayedover the media and flows through the tower.Oxidation occurs in both the falling liquid filmand in the attached growth. Less sludge isproduced from ABF treatment, diminishing thesize of the final clarifier. Reduced life-cycle andland costs, compensate for high capital cost. ABFtreatment achieves the same degree of effluentquality as activated sludge process (39). Biologi-cal towers can be designed and operated with thesame parameters as activated sludge systems.ABF’s are used for both domestic and industrialapplications.

(4) Anaerobic denitrification filter. Denitrif-ication in attached growth anaerobic reactors hasbeen accomplished in a variety of column configu-rations using various media to support thegrowth of denitrifying bacteria. In the deni-trification column, the influent wastewater isevenly distributed over the top of the mediumand flows in a thin film through the medium onwhich the organisms grow. These organismsmaintain a balance so that an active biologicalfilm develops. The balance is maintained bysloughing of the biomass from the medium, eitherby death, hydraulic erosions or both. Sufficientvoids are present in the medium to preventclogging or pending. The denitrification columnmust be followed by a clarification step to removesloughed solids. The various types of denitrifica-tion columns currently available are summarizedbelow:

–Packedporosity media.

–Packedmedia.

bed, nitrogen gas void space, high

bed, liquid voids, high porosity

–Packed bed, liquid void, low porositymedia.

–Fluidized bed, liquid void, high porosityfine media (sand, activated carbon).

Most denitrification work has been conducted onsubmerged columns wherein the voids are filledwith the fluid being denitrified. The submergedcolumns can be further subdivided into packedbed and fluidized bed operations. Recently, a newtype of column has been developed in which thevoids are filled with nitrogen gas, a product ofdenitrification.

d. Miscellaneous Biological Systems.(1) Package plants. A number of so called

“package plants” have been developed to servethe wastewater treatment needs of small installa-tions. Many of these units are available from anumber of manufacturers. The small ones are allfactory fabricated and shipped as nearly completeunits except for electrical connections and otherminor installation requirements. These will servea maximum population of 300 to 400. Largersized package plants are partially constructed inthe factory and then field erected. These types offacilities generally will serve larger installations,up to about 1 mgd. Package plants are availableas biological treatment facilities and some newunits have been developed for physical-chemicaltreatment applications. Nearly all of the biologicalunits use the activated sludge process, principallyextended aeration and contact stabilization modi-fications. The small physical-chemical packageplants have been developed mainly as “add on”units to existing biological facilities to provideadditional removal of organic and inorganic con-stituents. Physical-chemical package units areavailable for multi-media filtration, phosphorusremoval, nutrient removal and activated carbonoperations. For widely varying flows at smallinstallations, a battery of physical-chemical unitsmight be employed. The on-off operation of theseinstallations would not be satisfactory for biologi-cal units.

(2) Batch activated sludge. A batch activatedsludge system utilizes a single tank reactor. Thetypical treatment cycle consists of:

—fill, in which the wastewater is received.—react, which allows treatment reactions to

be completed.— settle, which separates the sludge from

the effluent.–draw, in which the effluent is discharged.—idle, the time period between discharge

and refill.A batch activated sludge system combines thereactor and clarifier into a single unit. Sludge

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TM 5-814-8

wastage can take place at either the end of thereact cycle or after the settling cycle, prior todraw off of the effluent. If required, a higherwastage concentration can be obtained throughdraw off of the settled solids. Effluent quality canbe considered essentially equal to conventionaltreatment, with its benefits being seen mainlywith smaller sytems requiring a relatively lowflow of wastewater for treatment.

(3) Sequencing batch reactors. The sequenc-ing batch reactor system ( SBR) uses two or moretanks with various functions operating in a se-quence. The typical treatment cycle consists ofthe same steps as a single batch activated sludgetreatment system, fill, react, settle, draw, andidle. The tanks fill in sequence in a multiple tanksystem, allowing for a joint reactor-clarifier unit.As with the batch activated sludge system,sludge wastage can occur from each reactor dur-ing either the react or settle mode. Vitrificationand dentrification are possible through systemmodifications. The SBR system is capable ofmeeting effluent requirements, with operationaland maintenance cost roughly equal to, and initialcost less than or equal to conventional systems(74).

(4) Septic system with recirculating sand fil-ters. A septic system with a recirculating sandfilter utilizes a conventional septic or Imhoff tankwith a sand filter instead of a tile field (166). Thesystem also includes a recirculation tank whichreceives effluent from the septic system as well asunderflow from the sand filter. Effluent from therecirculator tank is pumped to the filter on a timebasis. Float controls may also be required to keepthe recirculation tank from overflowing. The pur-pose of the recirculation tank is to keep the sandfilter wetted at all times. This system eliminatesthe odor problem common with intermittent fil-ters. This system is applicable for small domesticfacilities, recreational areas, etc.

(5) Overland flow. This technique is the con-trolled discharge, by spraying or other means, ofeffluent onto the land with a large portion of thewastewater appearing as run-off. Soils suited tooverland flow are clays and clay silts with limiteddrainability. The land for an overland flow treat-ment site should have a moderate slope.

e. Biological system comparisons. Table 6–4provides a comparison of the key wastewatertreatment processes which must be considered forpollution control programs at military installa-tions. These comparisons include major equip-ment required, preliminary treatment steps, re-moval efficiency, resource consumption, eco-

nomics and several other factors which must beconsidered.

6-3. Physical and Chemical Waste- water Treatment Processes

a. Introduction. Physical and chemical pro-cesses may be categorized as treatment for theremoval pollutants not readily removable orunremovable by conventional biological treatmentprocesses. These pollutants may include sus-pended solids, BOD (usually less than 10 to 15mg/L), refractory organics, heavy metals andinorganic salts. In domestic wastewater treat-ment, a physical-chemical process may be re-quired as tertiary treatment to meet stringentpermit applications. In industrial applications,physical-chemical treatment is frequently used asa pretreatment process in addition to its use as atertiary process. The primary physical-chemicalprocesses included in this manual are:

—Activated carbon adsorption.–Chemical oxidation.–Solids removal (clarification, precipitation).

Each of the treatment alternatives above, as wellas, other less common physical chemical processesare discussed in this section.

b. Activated carbon adsorption.(1) Description. Carbon adsorption removes

many soluble organic materials. However, some organics are biodegradable, but not adsorbable.These will remain in the effluent from physical-chemical systems. While carbon adsorption isused in physical-chemical secondary treatmentsystems, its most significant application is aspart of an advanced wastewater treatment sys-tem employing numerous schemes for additionalconstituent removal or as part of a systemtreating an industrial wastewater stream.

(2) Applications. Carbon adsorption has beenadequately demonstrated in numerous pilot andfull scale facilities as a system which can achievea high degree of organic removal to satisfy waterquality standards. The carbon adsorption processcan be readily controlled and designed to achievevarious degrees of organic removal efficiency.This feature makes it unique as an advancedwastewater treatment step. The activated carbonsystem is utilized to treat certain industrialprocess wastewaters from military installationsincluding munitions wastes.

(3) Design considerations. Both the powderedand granular forms of activated carbon can beused. However, powdered carbon currently cannotbe justified economically due to problems associ- ated with regeneration of the material; thus, thepresent state-of-the-art in activated carbon

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TM 5-814-8

Table 6.4. Summary of primary and biological wastewater treatment processes

Major Treatment PreliminaryUnit Process Purpose Equipment. Required Treatment Steps Application

Primary sedimentation tankwith sludge collectingmechanism and skimmingdevice.

Screening and usually gritremoval .

Almost all domestic waste-waters. Must precede trick-ling filter. Does not haveto precede activated sludge,but usually most economicalmethod of reducing BOD andsuspended solids.

Removal of carbonaceousBOO. Under certain environ-mental conditions mayachieve considerable nitri-fication.

Removal of carbonaceousBOO. Usually little nitrifica-tion unless designed for longsolids retention time.

Remove settleable suspendedinorganic and organic solids.

A. Primary Sedimentation

Must have primary treat-ment.

Biologically convert dis-solved and nonsettleableorganic material andremove by sedimentation.

Trickling filter, settlingtank and sludge collector,recirculation pumps (highrate units), and piping.

ter SystemsB. Trickling Fil

Aeration tank, aerationequipment, settling tank,sludge collector, sludgereturn pumps, and piping.

Usually primary treatmentalthough not necessary.

Biologically convert dis-solved and unsettleablesuspended organic materialand remove by sedimenta-tion.

c. Activated Sludge System

D. Ponds Small facilities where ade-quate land area is available.Good for intermittent waste-water discharge, but willnot meet U.S. EPA-defined secon-dary treatment standards.

Where ammonia conversionor nitrogen removal isrequired.

Earthen pond with inletand outlet structures.

None.Combines the purposes ofprimary and secondarybiological treatment aswell as sludge treatmentand disposal into one unitprocess.

Usually secondary treat-ment; although in manycases with proper designand operation, nitrifica-tion can be part ofsecondary treatment.

Biologically oxidizeammonia to nitrates.

1. Suspended GrowthSystem - vitrificationtank, aeration equipment,settling tank and sludgecollector. sludge returnpumps, and piping.

E. Vitrification(Nitrogen Conversion)

2. Tricklinq FilterSystem - low-rate filter,settling tank and sludgecollector.

3. Rotating BiologicalContactor System -several RBC stages, set-tling tank and sludgecollector.

F. Denitrification Where complete nitrogenremoval is required andvitrification facilitiesare installed. Potentialfor combining with fil-tration step is good.

Most be preceded byvitrification step.

Biological removal ofnitrogen by reductionfrom nitrates to nitrogengas.

1. Suspended Growthsystem - denitrificationtank with mixing equip-ment, final settling tankwith sludge collectionequipment, return sludgepumps and piping, chemicalfeed system, and possiblysmall aerated basin forrelease of nitrogen gas.

2. Columnar System -structure containing mediasimilar to deep bed filter(gravity or pressure sys-tem), backwash and chemi-cal feed equipment.

wastewater treatment is limited to granular car-bon. Both upflow and downflow carbon contractorscan be used. Upflow units more efficiently utilizecarbon since counter-current operation is closelyapproached. Downflow contractors are used forboth adsorption and some suspended solids filtra-tion. Dual-purpose downflow contractors offsetcapital cost at the expense of higher operatingcosts. The following basic factors should beconsidered when evaluating an activated carbonsystem (l)(127):

—To avoid clogging, the influent total sus-pended solids concentration to the acti-vated carbon unit should be less than 50mg/L.

–Hydraulic loadings and bed depth areimportant design parameters, but contacttime is the most important factor incarbon systems.

–For some domestic and certainly all in-dustrial applications, treatability studies,(laboratory and pilot scale) must be con-ducted. This is essential since the carbonremoves the dissolved trace organicsfrom wastewaters by a combination ofadsorption, filtration and biological degra-dation. Treatability studies will assist inevaluating these factors to optimize de-sign criteria for the particular wastewaterunder consideration.

c. Chemical oxidation.

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TM 5-814-8

Removes 40 to 60% ofsuspended solids and30 to 40% of BOO.

Capital costs are generally Very small power consump- Simple to operate and main-tain. Most operational laborassociated with sludgeremoval.

Sludge-solids con- Severe odor problemstent 3 to 6%. if sludge is not

removed periodically.

A.

B.

c.

D.

E.

F.

lower than secondary -

treatment. O&M costsare low.

tion for sludge collectionmechanism.

Overall BOD removal(including primarysedimentation) about85%. Effluent sus-pended solids 30 to50 mg/L. Unlesscovered, removalsdrop off consider-ably In winter.

O&M costs are quite low. Minimal power costs. Relatively simple andstable operation. Not aseasily upset as activatedsludge systems. Tends topass rather than treatshock loads.

Sludge - humus that Filter flies thatsloughs off filter breed in filtermedium is generally medium. Potentialreturned to primary odors if overloadedsedimentation. or improperly main-

tained.

Generally can remove90+% of carbonace -ous BOD. Effluentsuspended solidsusually are lessthan 30 mg/L.

O&M costs are consid-erably higher thantrickling filter system.

High electrical powerconsumption to oper-ate aeration equipment.

Requires more skilledoperation than tricklingfilter. Subject to upsetswith widely varying organ-ic load, but can handleand treat shock loads.

Sludge - considerably None if properlymore than trickling operated. Potentialfilter system. Low odors if improperlysolids content (0.5 operated.to 1.0%).

None except land.Removes 99+% of ori-ginal BOD, but algaein effluent may re-sult in suspendedsolids (100 mg/L)and BOD (30 mg/L).High vitrificationduring warm weather.Must provide winterstorage; no treat-ment during icecover.

Greatly dependent onenvironmental factorssuch as temperatureand pH. Can reacheffluent ammoniaConcentrations downto 1 to 2 mg/L.Also removes muchof the carbonaceousBOD remaininq fromsecondary treatment.

Relatively low construc-tion cost and very lowO&M costs.

Minimal operation. Closeeffluent lines during icecover and retain all waste-water until spring thaw.

None. Odor problems duringspring thaw as pond isturning from anaerobicto aerobic conditions.

Costs similar to theappropriate secondarytreatment system (acti -vated sludge, tricklingfilter, RBC).

High power consumptionin suspended growthsystem.

Generally requires super-vision equivalent to theappropriate secondarytreatment process.

Almost negligible None if properlysludge production. operated.

A relatively small None apparent atamount of waste time.sludges are generatedin suspended growthsystem and coarsegrain columnar system.Backwash water infine grain columnarsystem.

Nitrates (as nitro-gen) can be reducedto below 1 mg/L.Columnar system withfine grain mediaalso can double asfilter with appro-priate suspendedsolids removal.

High construction costs.O&M costs relatively highdue to carbon sourcesuch as methanol thatusually is added to sys-tem.

Chemical use such asmethanol; miminal powerconsumption.

Requires skilled opera-tion, careful control ofmethanol feed, and sys-tem monitoring.

(1) Chlorination. Chlorine is the principalchemical utilized for disinfection in the U.S.Chlorine dosages vary, but for secondary treat-ment effluents the normal range is from 5 to 15mg/L with requirements for a chlorine residual ofnot less than 0.2 to 1.0 mg/L after a 15 minutedetention time at maximum flow rate (108).Regulatory requirements may differ in variousStates and consultation with the appropriateagency is recommended. Disinfection must meetthe U.S. EPA fecal coliform level of 200/100 mL.General practice is to provide the chlorine feedeither as gaseous chlorine, normally vaporizedfrom l iquid s torage , or f rom a ca lc iumhypochlorite solution feeder. Other than for ex-tremely small plants, the gaseous chlorines moreeconomical. However, many of the large metropol-itan areas, such as New York and Chicago, have

converted to the use of hypochlorite solutions dueto the potential hazards involved in transportingchlorine through populated areas. Where treat-ment facilities are remotely located, such as manymilitary installations, gaseous chlorine will beacceptable provided suitable safety precautionsare taken with shipping and handling. Possibledisadvantages of chlorine disinfection are thetoxicity of the chlorine residual to aquatic life andthe potential of the chlorine combining withorganic material in the effluent or the receivingstream to form cancer-causing compounds. SomeStates and the U.S. EPA have proposed limita-tions on the residual chlorine concentration inboth effluent and streams. Thus, for some chlori-nation systems additional detention time, addi-tion of a reducing agent (sodium bisulfite or sulfur dioxide), or passage through activated

6-16

TM 5-814-8

carbon may be required to reduce chlorine residu-als prior to discharge.

(2) Alkaline chlorination. Use of breakpointchlorination to oxidize ammonia to nitrogen gas,which is released to the atmosphere, has beenused in water treatment for numerous years. theprocess requires large chlorine dosages (8 to 10mg/L chlorine for each mg/L of ammonia oxidized)resulting in high operating costs. Adjustment ofpH is often required and formation of complexorganic-nitrogen-chlorine compounds have beenharmful environmental effects. Application will belimited to removal of trace ammonia after someother ammonia removal process.

(3) Ozonation. An alternative to chlorine isuse of another disinfectant such as ozone. Manu-facturer’s literature indicate over 500 water treat-ment plants in Europe use ozone for disinfection.Chlorine, however, remains the predominant disin-fectant for portable water in the U.S. Althoughozone has had limited application in wastewatertreatment, equipment manufacturers and otherliterature report many pilot studies have beenand are currently being conducted. Results indi-cate ozone is an effective disinfectant forwastewater effluents. Use of ozone avoids theproblems with aquatic life and disinfects at afaster rate than chlorine. Ozone, however, is 10 to15 times as expensive as chlorine and on-sitegeneration is necessary (80).

(4) Hydrogen peroxide oxidation. Hydrogenperoxide (H202) is a strong oxidizer but has onlylimited application in the disinfection ofwastewater. This is primarily because three tofour hours of contact time is required to accom-plish disinfection and it tends to leave a distinc-tive taste. The primary use of hydrogen peroxidesis in industrial applications where it is extremelyeffective in oxidizing a wide variety of pollutants.Uses include destruction of cyanide which isgenerated from electroplating and destruction oforganic chemicals including chlorinated and sulfurcontaining compounds and phenols. Hydrogenperoxide is clear, colorless, water like in appear-ance and has a distinctive pungent odor. Hydro-gen peroxide is not a hazardous substance and isconsiderably safer to handle and store than chlo-rine gas.

(5) Ultraviolet radiation. Ultraviolet radiationis a very effective alternative to chemical oxida-tion. This method consists of exposure of a filmof water up to several inches thick to quartzmercury-vapor arc lamps emitting germicidal ul-traviolet radiation. This technique has been re-ported to have been used on small systems inEurope for over 100 years. Although this alterna-

tive is receiving attention as an alternate, itremains unattractive due to high capital andoperating costs for other than very small sys-tems.

(6) Ionizing radiation. Application of ionizingradiation as an alternative to chlorine or ozone fordisinfecting wastewater and as an alternative toheat for disinfecting sludge is now in the develop-ment and demonstration stage in the U.S. and inEurope. Both gamma rays and high energy elec-trons are being evaluated. The technical feasibil-ity has been established but data to assess thecost-effectiveness are not yet available. Experi-ence to date with ionizing radiation indicates thatapplications will be characterized by relativelyhigh capital costs and moderate-to-low operatingcosts. In addition to destroying microorganismsin wastewater and sludge, ionizing radiation hasshown capabilities of reducing concentrations ofphenol and surfactants, increasing settling ratesand destroying chlorine in wastewater, and im-proving physical characteristics of sludge. Engi-neers concerned with either upgrading existingwastewater treating facilities or designing newfacilities should be aware of this developing areaof potentially applicable technology. Reference toavailable literature or contact with HQDA(DAEN-ECE-G) WASH DC 20314, is suggested,Authority to apply this emerging technology inany waste treatment process must be obtainedfrom DAEN-ECE-G.

d. Solids removal.(1) Chemical precipitation phosphorus re-

moval.(a) Description. Phosphorus removal is

needed because it is a major nutrient for algaeand other aquatic vegetation. The sources ofphosphorus in a typical domestic wastewater fora military facility are associated with humanexcretions, waste foods and laundry products.While conventional wastewater treatment tech-niques, i.e., primary sedimentation and secondarytreatment, will remove about 10 to 40 percent ofinfluent phosphorus, it often becomes necessaryto provide for additional removal to meet effluentor water quality criteria. Numerous States in theU.S. have developed water quality criteria and/oreffluent standards for phosphorus. Typical limita-tions are 1 to 2 mg/L. However, recent standardsbeing considered by regulatory agencies indicatelevels for given situations may become morestringent. The U.S. EPA should be contacted forrequirements when wastewater treatment facili-ties alternatives include phosphorus removal.

(b) Application. Some biological techniquesfor removing phosphorus have been identified,

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TM 5-814-8

but no large scale or long term demonstrations ofthe process have been undertaken. The commonmethod of removal is by chemical treatmentusually employing alkaline precipitation with limeor precipitation using minerals (iron or aluminumsalts). The process can be accomplished in numer-ous ways either in the primary system, secondarysystem or as a separate system. The particularmethod to employ at a given installation is amatter of numerous constraints. The two predom-inant methods are mineral addition to the pri-mary clarifier and lime clarification after second-ary treatment, although addition of minerals orlime to the final clarifier of trickling filter sys-tems has been successful. Mineral additions tothe primary or secondary clarifier will not usuallyprovide quite as low a phosphorus level as limeprecipitation. All precipitation processes increasesludge quantities which must be handled.Recalcination of lime will not be economical atmost military facilities. Design considerations forthe various phosphorus removal alternatives arepresented in TM 5-814-3 and the U.S. EPAProcess Design Manual for Phosphorus Removal.

(2) Sedimentation.(a) Process description. Sedimentation is

the separation of suspended particles that areheavier than water from water by gravitationalmeans. It is one of the most widely used unitoperations in wastewater treatment. This opera-tion is used for grit removal; particulate-matterremoval in the primary settling basin; biological-floc removal in the activated sludge settlingbasin; chemical-floe removal when the chemicalcoagulation process is used; and for solids concen-tration in sludge thickeners. Although in mostcases the primary purpose is to produce a clari-fied effluent, it is also necessary to producesludge with a solids concentration that can beeasily handled and treated. In other processes,such as sludge thickening, the primary purpose isto produce a concentrated sludge that can betreated more economically. In the design ofsedimentation basins, due consideration should begiven to production of both a clarified effluentand a concentrated sludge (125).

(b) Clarifier design. Clarifiers may either berectangular or circular. In most rectangular clari-fiers, scraper flights extending the width of thetank move the settled sludge toward the inlet endof the tank at a speed of about 1 ft/min. Somedesigns move the sludge toward the effluent endof the tank, corresponding to the direction of flowof the density current. Circular clarifiers mayemploy either a center feed well or a peripheralinlet. The tank can be designed for center sludge

withdrawal or vacuum withdrawal over the entiretank bottom. Circular clarifiers are of three gen-eral types. With the center feed type, the waste isfed into a center well and the effluent is pulled off at the weir along the outside. With a peripheralfeed tank, the effluent is pulled off at the tankcenter. With a rim-flow clarifier, the peripheralfeed and effluent discharge are also along theclarifier rim, but this type is usually used forlarger clarifiers. The circular clarifier usuallygives the optimal performance. Rectangular tanksmay be desired where construction space is lim-ited. The circular clarifier can be designed forcenter sludge withdrawal or vacuum withdrawalover the entire tank bottom. Center sludge with-drawal requires a minimum bottom slope of 1in/ft. The flow of sludge to the center well islargely hydraulically motivated by the collectionmechanism, which serves to overcome inertia andavoid sludge adherence to the tank bottom. Thevacuum drawoff is particularly adaptable to sec-ondary clarification and thickening of activatedsludge. The mechanisms can be of the plow typeor the rotary-hoe type. The plow-type mechanismemploys staggered plows attached to two oppos-ing arms that move about 10 ft/min. The rotary-hoe mechanism consists of a series of shortscrapers suspended from a rotating supportingbridge on endless chains that make contact with the tank bottom at the periphery and move to thecenter of the tank.

(3) Microscreening. The use of microscreeningor microstraining in advanced wastewater treat-ment is chiefly as a polishing step for removal ofadditional suspended solids (and associated BOD)from secondary effluents. The system consists ofa rotating drum with a peripheral screen. Influentwastewater enters the drum internally and passesradially outward through the screen, with deposi-tion of solids on the inner surface of the drumscreen. The deposited solids are removed bypressure jets located at the top of the drum. Thebackwash water is then collected and returned tothe plant. The screen openings range from about23 to 60 microns depending upon manufacturertype and material. However, the small openingsthemselves do not account for the removal effi-ciency of the unit. Performance is dependent onthe mat of previously trapped solids which pro-vide the fine filtration. Thus an important factorin design is the nature of the solids applied to thesystem. The strong biological floes are better formicroscreening; weak chemical floe particles arenot efficiently removed. Depending upon the in-f l u e n t w a s t e w a t e r c h a r a c t e r i s t i c s a n d t h e microfabric, suspended solids removals have

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TM 5-814-8

ranged from about 50 percent to as high as 90percent. Maintenance of the units can be costly,since they require periodic cleaning. For furtherinformation, the U.S. EPA “Process Design Man-ual for Suspended Solids Removal”, and “ProcessDesign Manual for Upgrading Wastewater Treat-ment Plants”.

(4) Filtration. Secondary effluents normallycontain minerals which range from the easilyvisible insoluble solids to colloids. Filtration isone means of removing the suspended solids (andthe BOD associated with the suspended solids)remaining after secondary sedimentation to alevel which will meet effluent or water qualitycriteria. Filtration methods most applicable tomilitary facilities are the multimedia filter andthe diatomaceous earth system. For informationon design criteria and operating considerations,the U.S. EPA Process Design Manual for Sus-pended Solids Removal should be consulted.

(a) Multi-media. Recently, dual-media,mixed-media and multi-media filtration unitshave basically replaced the conventional singlemedium filter otherwise known as the “rapid-sandfilter” for wastewater applications. These filters,widely utilized in advanced wastewater treatment,are sometimes referred to as “deep-bed” filters.Single medium filters have a fine-to-coarse grada-tion in the direction of flow which results fromhydraulic gradation during backwash. This grada-tion is not efficient, since virtually all solidsremoval must take place in the upper few inchesof the filter with a consequent rapid increase inheadloss. A coarse-to-fine gradation, as used bymulti-media units, is more efficient since it pro-vides for greater utilization of filter depth, anduses the fine media only to remove the finerfraction of suspended solids. The multi-mediafilter is capable of producing effluents with sus-pended solids of less than 10 mg/L from typicalfeed concentrations of 20 to 50 mg/L. This alsoreduces the BOD since about one-half of theBOD of a secondary effluent is normally associ-ated with the suspended solids. The feed concen-tration must be kept below 100 mg/L of sus-pended solids for practical backwash cycles. Atypical multi-media system consists of three ormore materials, normally anthracite (coal), sandand garnet, with carefully selected specific gravi-ties. Dual-media filters usually utilize anthraciteand sand. The filtering system is supported by afew feet of gravel or other support means. Addi-tion of small amounts of coagulant chemicalssuch as alum or polymer enhances filtration.Multi-media filtration is a process normally asso-ciated either with physical-chemical wastewater

treatment or as a polishing step after biologicaltreatment. It is particularly applicable for re-moval of the weaker chemical floe particles whilesurface straining devices such as rapid-sand fil-ters and microstrainers work well with the stron-ger biological floes. Use of the filters for the dualpurpose of solids removal and as a fixed mediafor denitrification should also be considered whereboth processes are necessary. A summary ofinformation on effluent suspended solids to beexpected from a multi-media filtration system isindicated in table 6-5.

Table 6-5. Expected effluent suspended solidsfrom multi-media filtration of secondary effluent*

Effluent SuspendedEffluent Type Solids, mg/L

High-Rate Trickling Filter 10-20Two-Stage Trickling Filter 6-15Contact Stabilization 6-15Conventional Activated Sludge 3-10Extended Aeration 1--5

*Adapted from the U.S. EPA “Process Design Manual forSuspended Solids Removal”.

(b) Diatomaceous earth. Filtration bydiatomaceous earth consists of mechanically sepa-rating suspended solids from the wastewaterinfluent by means of a layer of powdered filter aidor diatomaceous earth, applied to a supportmedium. The use of the system for clarification ofdomestic secondary treatment effluent has beendemonstrated only at pilot scale facilities. Multi-media filters are more cost–effective for domesticwastewaters from military installations. However,the diatomaceous earth system is applicable andcurrently being used as part of a treatment stepin munitions wastewater treatment.

e. Membrane processes. Other feasible methodsof advanced wastewater treatment consist ofwhat are generally known as the membraneprocesses, and include electrodialysis, ultrafil-tration and reverse osmosis. These processes canremove over 90 percent of the dissolved inorganicmaterial to produce a high quality product suit-able for discharge or reuse. Considerable pretreat-ment is required. Use of these membrane pro-cesses in the field of wastewater treatment is atthe present time limited because the costs arevery high and applications will be to small flowsat best. For example, a possible application is thetreatment for reuse of small process discharges atmilitary field installations. Three different reverseosmosis units were evaluated at a field locationby the U.S. Army Environmental HygieneAgency (1). This study was initiated to determinethe feasibility of treating and reusing wastewaterfrom field laundries, showers and kitchens. Where

TM 5-814-8

it may be necessary to consider the application ofa membrane process for reuse or discharge, refer-ence should be made to appropriate design manu-als or manufacturer’s literature for information ondesign criteria.

f. Physical and chemical process comparisons.Table 6-6 provides a comparison of the keywastewater treatment processes which must beconsidered for pollution control programs at mili-

ing or equipment maintenance, the major portionof wastewater produced at a military installationwill be domestic waste similar in characteristicsto that produced in a residential area. However, for those installations with industrial facilities,certain process wastes produced on-site requireseparate consideration. The following are exam-ples of these waste producing processes:

–Munitions manufacturing, loading, assem-tary installations. These comparisons include ma- bling and packing.jor equipment required, preliminary treatment –Metal plating.steps, removal efficiency, resource consumption, –Washing, paint-stripping and machiningeconomics and several other factors which must erations.be considered. –Photographic processing.

6-4. Industrial process wastewater –Laundry.Other process waste sources include hospitals and

treatment blowdown from cooling towers, boilers and gas-a. Introduction. Except at those facilities where scrubber systems. Chapter 3 of this manual

the principal function is manufacturing, process- describes typical industrial waste producing pro

Table 6-6. Summary of physical and chemical wastewater treatment processes

Major Treatment PreliminaryUnit Process Purpose Equipment Required Treatment Steps Application

At least secondary treat-ment. Nitrogen must be inammonia form. The higherthe degree of treatment,the less chlorine requiredto reach breakpoint.

A. Breakpoint Chlorinationfor Ammonia Removal

Removes nitrogen by chemi -tally concerting to nitro-gen gas. Process also servesas disinfection step.

Chlorine contact basins andchlorination equipment mayrequire carbon adsorptionstep to remove potentiallytoxic chloro-organiccompounds formed.

Nitrogen removal . Hiqhchemical costs and sideeffects make process mostattractive as a back-upsystem in case of failure ofprimary nitrogen removalprocess and for removal ofremaining trace ammoniaconcentrations.

Where standards requireover 90% phosphorus removal,or phosphorus concentrate ionsbelow 0.5 mg/L, or as an ad-ditional step for suspendedsol ids removal. Recalcinationof lime sludge generally un-economical in plants under10 mgd capacity.

B. Lime Clarification Primary purpose is tochemically precipitatephosphorus. Secondarypurpose is to remove sus-pended solids and associ-ated BOO.

Clarifier, usually solidscontact up-flow type, withsludge collection equip-ment; chemical feed equip-ment; and recarbonationfacilities. Low alkalinitywastewaters may requiretwo-stage system withtwo clarifiers. Lime recal -cining furnance and re-lated equipment may beused for large facilities.

Chemical feed equipment,mixing and flocculatingbasins for existing pri-mary sedimental ion basins.

Usually secondary treat-ment although lime clari-fication of raw wastewateris practiced in physical-chemical plants.

c, Mineral Addition toPrimary Sedimentation

Primary purpose is tochemically precipitatephosphorus. Secondarypurposes are increasedsuspended sol ids and BOOremoval in primary sedi -mentation, thereby de-creasing the load onsecondary treatmentfacilities.

Suspended sol idsremova 1.

Screening and usual1 ygrit removal.

D. Multi-Media Filtration Filters and backwashequipment.

Generally at least sec-dary treatment.

E. Microscreening Suspended sol ids removal. Microscreens and tanks. Seconary treatment.

F. Granular CarbonAdsorption

Carbon contractors, carbonregeneration furnance,and carbon storagefacilities

1. AWT - secondarytreatment followed byfiltration for down-flowcontractors. Filtrationnot necessary for up-flowcontractors.

2. PCT - chemicalcoagulation of rawwastewater.

1. AWT - to remove traceorganic and produce highquality effluent.

2. PCT - remove carbon-aceous BOD as in secondarybiological treatment.

2. PCT - remove organicmaterial instead of bybiological treatment.

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TM 5-814-8

None. Adds cnnslderabl(]anuunt of chlori(lesto wastewater.

A.

B.

trol dose and PH. Mayrequire addition of chem-icals to control PH.

very small-amountswith regeneration.

cesses, waste characteristics. This section de-scribes waste reduction and treatment methodol-ogy applicable to military installations.

(1) Considerations. The need to consider in-dustrial process wastes separately is based on thefollowing potential effects:

—Degradation of the sewer lines by corro-sion or chemical attack and/or productionof an environment dangerous to mainte-nance and operating personnel.

–Interference with normal treatment plantprocesses.

–Inability of treatment plant processes toreduce a process waste constituent to alevel required by regulatory constraintsor other environmental considerations.

(2) Limitations. Brief descriptions of pro-cesses are included in chapter 3 to serve as abasis for consideration of the effect of suchwastes on facility planning. Typical analyses of

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TM 5-814-8

some process wastes are also provided. Thequantity and quality of process wastes producedoften vary in similar installations; therefore, datapresented are descriptive only. To establish basicdesign criteria, more detail is required. The appli-cability of the wastewater treatment and sludgedisposal processes presented elsewhere is dis-cussed for each special process in this section.

b. Munitions wastes. Wastes generated fromthe munitions industry originate from both manu-facturing (MFG) plants as well as loading, assem-bling and packing (LAP) facilities.

(1) Explosives and propellants. The majorexplosive product produced is trinitrotoluene(TNT). Other explosive chemicals that are gener-ated in military installations include:

—nitroglycerine.—HMX and RDX.—tetryl.—nitrocellulose.—black powder.—nitroguanidine.—lead azide.—lead styphnate.

A description of the manufacturing process uti-lized for each explosive, as well as typical waste-water characteristics are included in chapter 3.

(a) Waste reduction. Process changes toinclude increased chemical recovery/reuse andgood housekeeping are important waste reductionpractices in the manufacture of explosives andpropellants. For examples, as indicated in chapter3, changing from batch-type to continuous TNTmanufacturing resulted in lower chemical andwater usage and reduced waste volumes (20)(23)(116). High pressure water sprays also may resultin decreased cleanup water usage. Batch-dumpingof process wastes and acids must be discouraged.Whenever cooling water is reasonably uncontami-nated, it should be segregated from the contami-nated water streams, thereby reducing the vol-ume of waste to be treated.

(b) Sampling and gaging. Care must betaken in establishing a sampling program forexplosives manufacturing wastes which will accu-rately represent the waste flow and characteris-tics. This is necessary because of the difference inwaste characteristics from different manufactur-ing plants, even if they are making the sameproduct. Batch dumping, periodic cleanup opera-tions and changes in production levels all contrib-ute to wide variations in flows and concentra-tions. Such variations can result in the need foradded treatment capacity and/or provision forequalization storage. Cost-effective design andoperation of treatment equipment depend on

accurate assessment and management of wasteflow and quality.

(c) Environmental impact. The blood-red color from red water produced in TNT manufac-ture and fish kills resulting from high acidconcentrations are the most readily visible envi-ronmental impacts of improperly treated explo-sive wastes. High oxygen demand, excessive ni-trate compounds, elevated temperature and highsuspended solids also contribute to the gradualdegradation of the receiving body of water.

(d) Treatability. Explosives manufacturingwastes are sometimes toxic to conventional bio-logical treatment plants, but may be treated byphysical and chemical methods and by specificallyadapted biological means. Waste acids may beneutralized with lime or other alkaline materialusing conventional pH control methods. Acti-vated carbon adsorption has been successful forremoving color-causing TNT compounds as wellas HMX and RDX (20)(116)(130). The acidicwastes must not be neutralized with lime untilafter carbon treatment, because color removalefficiency is greater at low pH, and precipitatesformed by lime addition will encrust and clog thecarbon column. Color may also be removed by ionexchange, although problems exist with resinregeneration. Wastewater from an acid plant in aTNT manufacturing complex has been success- fully treated by lime precipitation followed by ionexchange (11 5). Biodegradable explosives wastes,including dynamite, nitrocellulose, HMX andRDX and TNT to some extent, may be treated bybiological methods such as land irrigation oractivated sludge after process proof by bench andpilot scale studies (77)(106)(107). Lead resultingfrom the production of lead azide and leadstyphnate may be removed by chemical precipita-tion using sodium sulfhydrate.

(e) Red water treatment. Red water is cur-rently one of the most difficult disposal problems.Red water has been sold to kraft paper millswhen transportation costs make this economicallyfeasible. In other cases, it has been burned in anincinerator. Where land permits, evaporationponds have been used; care must be taken toeffectively line the pond to prevent ground watercontamination from leaching. Fluidized bed incin-eration and recycle of the resultant ash are beingstudied (87).

(2) Projectiles and casings. The manufactureof the lead slugs, bullet jackets and shell casingsgenerates wastewater different in compositionthan from explosives manufacture. Waste constit- uents include heavy metals, oil and grease, soapsand surfactants, solvents and acids.

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TM 5-814-8

(a) Waste reduction. Waste reduction prac-tices which should be evaluated include use ofcounter-current flow of successive rinse waters,separation and reuse of lightly contaminatedwater (such as cooling water), elimination ofbatch-dumping of processing solutions, recoveryand reuse of metals and pickling liquor, andprovisions to divert highly contaminated spills toholding tanks for individual treatment.

(b) Gaging and sampling. Due to the ex-treme variations in flows and characteristics en-countered, careful sampling and gaging proce-dures must be employed in order to characterizethe waste and identify peak values. Identificationof peak values is helpful in tracing batch dump-ing and is essential to cost-effective design oftreatment facilities.

(c) Environmental impact. The environmen-tal impact of metal working wastes can be acute.Heavy metals, acids, surfactants and oils are allhighly toxic to aquatic life. Serious stream degra-dation results from the direct discharge of insuffi-ciently treated metal wastes.

(d) Treatability. Toxic materials present inthe wastewaters from munitions metal parts man-ufacturing can interfere with biological treatment.Treatment methods available include neutraliza-tion with lime, heavy metal removal and recoveryby precipitation or cementation, and oil removal

by gravity separation. Suitably pretreated wasteswill be cost-effectively treated along with domes-tic wastes in biological facilities (21).

(3) Loading, assembling and packing wastes.The main LAP operations are explosives receiv-ing, drying and blending operations, cartridge andshell-filling operations and shell-renovation. Themain waste sources are spillage, cleanup water,dust and fume scrubber water and waste flowsfrom renovation operations.

(a) Waste reduction. Waste reduction whichshould be considered in a pollution control pro-gram can be accomplished by reuse of lightlycontaminated water for air-scrubbing and shell-washout. In the shell-loading operation, the use ofcovered hot water baths and shell-loading funnelscan reduce or eliminate explosives contaminationof the water baths. High-pressure water sprayscan reduce the amount of water used for cleanup.Recovery of waste explosives from shell-washoutoperations reduces the waste load and is aneconomic incentive. Proper wastewater gagingand sampling practices can be quite helpful inidentifying the source of any unauthorized batch-dumps and lead to waste reduction practices.

(b) Environmental impact. The environmen-

tal impacts of LAP wastes include red colorationfrom TNT-containing wastewater, heavy metaltoxicity, oxygen depletion and toxicity and bittertastes from excess nitrates (11)(20).

(c) Treatability. LAP plant wastes havebeen treated successfully by diatomaceous earthfiltration followed by activated carbon adsorption.Effluents of less than 5 mg/L of TNT are readilyattainable. Suspended solids removals by thediatomaceous earth filters have, in some in-stances, been much less than expected. Presenceof suspended solids in waste entering the acti-vated carbon filter greatly reduces the effectivelife of the carbon unit due to clogging. Normally,the spent carbon is burned, although experimen-tal work is being performed to determine thefeasibility of regeneration in fluidized beds. Car-bon usage varies from 2 to 7.5 lb carbon/1000 gal(11)(20). Plating wastes from renovation opera-tions are treated in the manner described inchapter 3.

c. Metal plating. The major waste sources arerinse water overflow, fume-scrubber water, batch-dumps of spent acid, alkali, or plating bathsolutions, and spills of the concentrated solutions.

(1) Plating waste separation. Processing solu-tions are often replaced on an intermittent basis;consequently, dumps of spent solutions impose aheavy short term load on treatment facilities.Therefore, separate collection of waste processsolutions and rinse waters should be evaluated.Separation as to type of waste is also desirable tofacilitate later treatment and to avoid the produc-tion of the toxic hydrogen cyanide gas at low pHlevels. Categories for waste separation are asfollows:

—Oil bearing wastes from cleaning opera-tions.

—Acid wastes including waste pickling li-quor, acid-plating solutions, and anodiz-ing solutions.

—Alkaline wastes including cyanide-platingsolutions.

(2) Waste reduction practices. There are anumber of waste reduction practices which can beeffective and should be considered for platingoperations including: dragout reduction, process/chemical changes, and good housekeeping(35)(41)(111).

(a) Plating waste dragout reduction. Reduc-ing the dragout from chemical baths not onlyreduces the contamination of successive rinsewater, but it also prolongs the life of the chemicalbath. Some dragout reduction practices whichshould be evaluated are:

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TM 5-814-8

—Design special drip pans,fog-sprays, air knivesmechanisms.

high-pressureand shaking

— Improve racking procedures and mini-mize overcrowding on the rack to facili-tate drainage of process chemicals backinto the chemical tank.

—Increase drainage time over the processtank or install an empty tank upstreamfrom the rinse operation in which theprocess solution can be drained andreturned to the process tank.

–Reduce the viscosity of plating agentswith either water or heat.

—Add wetting agents to process solu-tions to reduce surface tension andfacilitate drainage.

(b) Plating process changes. Changes inprocess or chemicals used can result in a reducedwaste volume, reduced waste strength or a wastewhich is more readily treatable. Process/chemical changes include the following and shouldbe considered in pollution control evaluations:

—Eliminate use of breakable containersfor concentrated solutions.

—Employ a recovery step for metalsfrom the waste stream. This adds aneconomic incentive to cleanup the efflu-ent.

—Recirculate the water used in the fume-scrubber systems.

—Separate cyanide wastes from chro-mium bearing and other acid wastes toavoid production of lethal hydrocyanicacid fumes.

—Substitute high-concentration platingsolutions for low-concentration solu-tions, reducing the volume of waste tobe treated.

—Replace cyanide salt plating solutionswith low cyanide or cyanide-free solu-tions.

—Use counter-current rinse flows ratherthan using fresh water in all rinses.

(c) Plating waste reduction by other means.Good housekeeping steps are important wastereduction practices which should be employed forall industrial operations; those particularly impor-tant to plating include the following:

—Curb areas which have chronic spillageor leakage problems and divert spills toa holding tank for treatment.

— Increase inspection and maintenance ofpipes, valves and fittings to preventleaks and spills.

6 - 2 4

(3) Gaging and sampling. Because of theconcentrated processing solutions used and theirhighly variable characteristics, proper wastewatergaging and sampling is essential in determining the characteristics and sources of batch-dumpsand the resultant peaks. Sampling of effluentsfrom the individual waste sources can be animportant supplement to end-of-pipe data.

(4) Environmental impact. The extremes ofpH and the high concentrations of heavy metalsand cyanides are extremely toxic to all forms oflife. Fish kills and even fatalities to livestockhave been reported when plating wastes were feddirectly to a body of water (34). The accumulationof heavy metals in sediment causes long termpollution. In addition, toxicity to micro-organismsretards the self-purification abilities of the receiv-ing stream.

(5) Treatability. Plating wastes may betreated by conventional municipal biological pro-cesses if sufficient dilution is provided. Otherwise,the extreme toxicity of the waste will seriouslyinterfere with the biological processes. Just asheavy metals become concentrated in streamsediments, they also accumulate in treatmentplant sludge and can interfere with subsequentbiological treatment processes and disposal proce-dures. Pretreatment of industrial wastes to reduceconstituents to levels which will be compatible with biological treatment is required. Pretreat-ment requirements for plating wastewater toensure successful subsequent treatment with do-mestic waste may require pilot scale studies(34)(76)(78). The pH control, cyanide destructionand heavy metal removal/recovery methods dis-cussed in chapter 3 are capable of providing therequired pretreatment for discharge to a biologi-cal treatment system or directly to a receivingbody of water. Such treatment may also permitrecycling and reuse of the water for some processneeds. In many cases, it is desirable to integratethe treatment operations into the overall platingscheme (33)(109).

d. Washing, paint-stripping and machining.Washing and paint stripping of aircraft and landvehicles is performed as routine maintenance or inpreparation for repairing, overhauling and ma-chining of a part or component of the aircraft orvehicle.

(1) Waste reduction practices. The volume ofwashrack and paint-stripping wastewater to betreated can be reduced considerably by excludingstorm water and by employing practices to reducethe amount of water used. It is reported that some U.S. commercial airlines have used hot,rather than cold, water sprays in the paint-

TM 5-814-8

stripping operation, resulting in a water usage ofonly four gallons per gallon of stripper. Also,squeegees are used to remove the paint-stripperand paint skins onto plastic sheets which aredisposed of at a sanitary landfill (29).

(2) Gaging and sampling. Care must be takenwhen sampling wastewaters with high oil con-tents, such as washrack and paint-strippingwastes, to ensure that a representative sample isobtained (15 1). The precaution is required due tothe tendency of oil to float on the water surface.

(3) Environmental impact. Washrack andpaint-stripping wastewaters containing high con-centrations of phenols, organic solvents, chro-mium, oils and surfactants are extremely toxic toaquatic life. Failure to properly contain and treatthese wastes can result in fish kills, streampurification inhibition and odors. All of these areunacceptable by any water quality standards(26)(29)(1 13). Oils from machining operations canbe toxic and may impose a high oxygen demandon the receiving body of water.

(4) Treatment. Unless highly diluted, the rawwastewaters from machining and paint-strippingoperations and washracks utilizing solvents arehighly toxic to the microorganisms of biologicaltreatment plants, interfering with both aerationand sludge digestion processes. Paint-strippingwastes are particularly toxic. A typical pretreat-ment system for a major facility would includethe following steps:

–Gravity separation tank equipped to re-move floating oils and settleable solids.

–Detention tanks with mixing to provideequalization of flow and waste strengthas well as to permit evaporation of vola-tile solvents.

–Chemical addition in a rapid mix tankfollowed by slow mixing in a separatetank to promote flocculation, break emul-sions and agglomerate solids.

–Final treatment in an air flotation unit toremove flocculated particles.

For smaller facilities, where washrack wastes areonly a small part of the total waste flow, analternate approach can be used. A storage tank,arranged to receive this waste and equipped withair mixing and adequate air emission controls,would provide for evaporation of a part of thevolatile solvents and permit pumping to the mainsewer at a controlled rate. At the main treatmentplant, the primary settling tank preceding biologi-cal treatment will have adequate oil and solidsremoval capacity.

e. Photographic processing. Because of thewidespread use of photography in military opera-

tions, the military services operate many photo-processing facilities. The size of such facilitiesvaries greatly, with waste flows of 10,000 to1,000,000 gallons per month. Liquid wastes origi-nate from the discharge of spent processingsolutions and associated rinse or washwaters.Approximately 90 percent of the liquid wasteproduced is from the rinse operations.

(1) Waste reduction practices. Waste reduc-tion practices include recovery of silver, regenera-tion of ferrocyanide and other chemicals, chemicalbath reuse and the use of squeegees to reduce thecarryover, or dragout, of chemicals from one stepto another.

(a) Silver recovery. Because of the highmarket value of silver, it can be economicallyrecovered from the spent bleach and fixer solu-tions as well as from the final washwater. Suchrecovery reduces the impact of silver as a pollut-ant and in some cases allows the fixer solution tobe reused, reducing chemical replacement costs.Silver recovery is most often accomplished bypassing the waste effluent through a proprietarysteel-wool-filled canister where silver is exchangedfor iron. Silver can also be removed by precipita-tion with sodium sulfide or by electrolysis.

(b) Bleach regeneration. The bleach solutionmay also be reused by regenerating ferrocyanidefrom the spent ferrocyanide using oxidizingagents such as persulfate and ozone. One manu-facturer offers a packaged bleach regeneratormaterial (123). Regeneration provides a cost sav-ings as well as pollutant reduction. Methods ofcomplete cyanide destruction are discussed laterin this chapter.

(c) Equalization. Equalization is very im-portant if photographic wastes are treated biolog-ically, particularly when the photographic pro-cessing operation occurs during only part of theday. Daily variations in flow and concentrationcan cause serious operating difficulties at thetreatment plant.

(2) Gaging and sampling. To define waste-water quality and quantity for a new installation,sampling and gaging data from a similar operat-ing facility is valuable. The presence of a largeamount of free silver metal will inhibit biologicalaction and yield unreliable BOD test data. Largeamounts of thiosulfates from the fixing bath willexert an oxygen demand. Care must be taken toprepare appropriate waste dilutions to avoid theseinterferences with the BOD tests.

(3) Environmental impact. The environmentalimpact of discharging improperly treated photo-graphic waste can be severe due to high concen-

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TM 5-814-8

trations of toxics. Heavy metals such as silverare toxic to aquatic life and can accumulate insediments. Cyanides, strong reducing agents andconstituents with high oxygen demands are allcapable of seriously degrading water quality.

(4) Compatibility with domestic wastewatertreatment. Experimental work has shown thatphotographic processing wastewater is treatableby biological means. One survey (30) indicatedthat almost 80 percent of Air Force base photo-graphic facilities discharge all or part of theirwastes to sanitary sewers. The Air Force Envi-ronmental Health Laboratory at Kelly AFB rec-ommended disposal of desilvered photographicwastewater in trickling filter or activated sludgeplants in proportions not exceeding 0.05 percentof the total waste influent. It is further specifiedthat the plant should discharge to a streamproviding a dilution of at least ten to onehundred times, to account for the conversion offerrocyanide to toxic cyanides. Mohanro, et al.,(75) chemically treated photographic wastes withalum to reduce the COD by 40 percent, thenpolished the effluent in activated sludge units.With roughly a two to one ratio of domesticsewage to chemically treated photographic waste,90 percent BOD reductions were obtained. Dagon(70) reported on a 20,000 gal/day package acti-vated sludge plant operating totally on rawphotographic wastewater and obtaining as muchas 85 percent BOD reduction. However, problemswere experienced with poor sludge settling. There-fore, it is generally recommended that photo-graphic wastes be treated witih domestic sewagein a biological plant after providing silver recov-ery and bleach regeneration; the photographicwaste portion should be kept to less than 20percent of the total. Bench scale or pilot planttesting may be required to define the treatmentapproach in some instances.

f Laundries. Central laundering facilities areprovided at most military facilities. At facilitiesengaged in industrial-type operations, additionalpollution problems may result from the launder-ing of the employees’ work clothes.

(1) Waste reduction practices. In recent yearsa variety of different synthetic laundry deter-gents have been used. Biodegradable detergentshave replaced “hard” detergents. In some areas,low phosphate or non-phosphate detergents havereplaced the established high phosphate com-pounds. The type of detergents used does warrantsome consideration because of treatment require-ments to meet regulations covering effluentcharacteristics.

(2) Gaging and sampling. Gaging and sam-pling of laundry wastewaters present no particu-lar problems. However, due to the differing char- acteristics of the various laundering processesand wash cycles within a process, some care mustbe taken in order to obtain representativewastewater samples.

(3) Environmental impact. The older “hard”synthetic detergents such as alkyl benzene sulfon-ates (ABS) were resistant to degradation bybiological means. Thus, they were dischargeduntreated to bodies of water, causing foamingproblems. Currently used biodegradable deter-gents such as linear alkylbenzene sulfonate (LAS)have eliminated this problem. These detergentsare biodegradable and exert a BOD in addition tothat of the soil, grease, starch and other materialswashed from the soiled garments.

(a) Phosphate. There has been a greatamount of controversy about the contribution ofdetergent phosphate compounds toward theeutrophication of lakes and rivers. Some statesand cities have banned the use of phosphate-containing or high-phosphate detergents. The en-vironmental effects of phosphates or the elimina-tion thereof are still unresolved.

(b) Explosives. In explosives manufactur-ing or LAP facilities, the laundering of employ-ees’ work clothes can create “ p i n k w a t e r ” c o n - lamination of the laundry effluent, with theresultant toxic effects and undesirable aestheticconditions.

(4) Treatability. Laundry wastewaters maygenerally be treated with domestic sewage byconventional biological systems. Due to the highlevels of emulsified grease, BOD and phosphates,special primary treatment, or pretreatment at thelaundry, may be required depending on the rela-tive proportion of laundry flow to total plantflow. Chemical precipitation and flotation havebeen used successfully as pretreatment (103)(130).Because surfactants (ABS and LAS) interferewith oxygen transfer, special care should be takento ensure that biological processes are receiving asufficient oxygen supply. When phosphorus re-moval is required, chemical precipitation pro-cesses should be employed.

(a) Unacceptable treatment. Laundrywastewaters should not be treated anaerobically,as in a septic tank-drainage field system. Thesynthetic detergents are not broken down and aretherefore more likely to enter water supplies.There is evidence that the detergents may also facilitate the movement of coliform bacteriathrough the soil (25).

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TM 5-814-8

(b) Treatment and recycle. Laundry waste-waters may be treated in commercially availablephysical-chemical units with the possibility ofrecycling the effluent. One system involves chemi-cal precipitation with alum, followed by sandfiltration, carbon adsorption and ion exchange.Another system consists of chemical precipitationand diatomaceous earth filtration. About 94 per-cent phosphate removal, 90 to 98 percent ABSremoval, 60 to 80 percent COD reduction and 60to 70 percent BOD reduction can be obtained (35).

g. Other generators. Other wastewaters typicalof some military facilities include hospitals dis-charges, boiler water blowdown, cooling watersystem blowdown, blowdown from boiler flue gas-scrubber systems and vehicle washing facilities.

(1) Hospitals. Hospital wastewaters requirespecial attention because of several factors. Thediurnal peaks and minimums of both flow andconcentration may be different from those nor-mally associated with domestic wastewaters dueto the unique hospital patterns of activity. Patho-genic organisms will probably be present inhigher than normal concentrations; however, mod-ern biological or physical-chemical secondarytreatment plants with post-chlorination shouldeliminate excess pathogens in the effluent. Con-servative design of chlorination facilities is en-couraged. Operating personnel must exercise spe-cial care to reduce the possibility of infection.Ample design and maintenance of screeningequipment should be exercised to eliminate mostproblems caused by excessive quantities of gauze,rags and bandages in the wastewater. Averagesewage flows from hospitals are estimated atabout 100 gallons per resident per day in TM5-814-1, while other sources estimate as high as200 gallons per bed per day. These values arequite similar to those for normal domestic sew-age. Resident population includes patients andfull time employees.

(2) Boilers. This waste is normally hot, up to210 degrees F, and contain phosphates (30 to 60mg/L), sulfite (30 to 60 mg/L), organic matter andsome suspended material. Normally, blending thiswater with other wastes reduces various constitu-ents to a level which will not inhibit subsequentbiological treatment. Direct discharge of blow-down to a receiving stream would require treat-ment to reduce phosphate and sulfite concentra-tions. In addition, cooling would be required fordirect discharge.

(3) Cooling water systems. Cooling water sys-tems can be classified in these general categories:

–Once-through systems.–Closed systems.

—Evaporative recirculating systems.(a) In once-through systems, the cooling

water is obtained from a lake or stream andreturned to the same stream with little or notreatment. Periodic additions of biocides aresometimes required to prevent fouling of thecooling water equipment. Chlorine is the mostcommonly used biocide. In some instances, thewater may require de-chlorination prior to returnto the stream.

(b) Closed cooling systems are used wherethe composition of the cooling water is critical,such as in the cooling of high temperaturesurfaces. The cooling water rejects heat to anair-cooled radiator or through a heat exchanger toa once-through or evaporative recirculating sys-tem. Blowdown or other losses from a closedsystem are small but contaminated. Corrosioninhibitors sometimes contain chromate, zinc, so-dium nitrate, and borax which must be removedprior to biological treatment or stream disposal.

(c) The evaporative recirculating systemuses a cooling tower or spray pond to dissipateheat by evaporation of a part of the flow.Although limited by blowdown, this results in anincrease in the concentration of dissolved solidsto a level of 3 to 5 times that found in themakeup water. To avoid corrosion, scale andbiological problems, acid, inhibitors and biocidesare added to the system. Treatment of theblowdown is sometimes necessary for removal ofany chromate, zinc compounds or other materialsused as an inhibitor.

(4) Scrubber systems. Scrubbers are used toavoid air pollution. Airborne wastes, accumulatedby the recirculating liquid, require that the liquidbe periodically or continuously treated for re-moval of wastewater constituents. In scrubbingof boiler stack gases, fine ash and sulfur oxidesmust be removed or neutralized. Other scrubbingsystems have similar treatment requirements.

h. Treatment methods. Special treatment pro-cesses are required for some industrialwastewater constituents. These processes may beemployed to provide for pretreatment prior tomixing with other wastes for completewastewater treatment and discharge, or for recov-ery of special constituents.

(1) pH control. For discharging wastewaterto a biological treatment process or directly to areceiving stream, pH must generally be main-tained in the range of 6.0 to 9.0; although limitsmay be much closer in certain instances. Treat-ment processes to destroy cyanides, to reducehexavalent chromium and to precipitate heavymetals also require pH control.

6 - 2 7

TM 5-814-8

(a) Acid waste neutralization. Neutraliza-tion of an acid waste (low pH) can be accom-plished by adding alkaline materials such ascrushed limestone, lime, soda ash or sodiumhydroxide to the acidic waste. Limestone (CaCO3)neutralization of a waste containing sulfuric acidforms a salt of limited volubility (CaS04) which cncause adherent deposits on equipment surfacesand piping. Hydrated lime (Ca(OH)2) or quicklime(CaO) are more commonly used, since these mate-rials have more neutralizing capacity per poundthan limestone. However, lime may also formcalcium sulfate sludges. Strong bases such assoda ash (Na2C03) or sodium hydroxide (NaOH)quickly neutralize strong acids, forming solublesalts and virtually eliminating the sludge prob-lem, although increasing the dissolved solidscontent of the water. Strong bases require specialequipment and handling and are four to eighttimes as expensive as lime or limestone.

(b) Alkaline waste neutralization. Neutral-ization of an alkaline or basic wastewater (highpH) can be accomplished by adding acidic materi-als such as carbon dioxide (CO2) or sulfuric acid(H2S04). Carbon dioxide may be added by passingboiler flue gas or bottled CO2 gas through thealkaline waste, forming carbonic acid (H2C O3)which then neutralizes the base. Sulfuric acidreadily neutralizes bases, although it is highlycorrosive and requires special equipment andhandling. Other strong acids, such as hydrochlo-ric acid (HC1), can be used depending on acidcosts.

(2) Heavy metal removal and recovery.Heavy metals which are of most concern aresilver (Ag), cadmium (Cd), chromium (Cr), copper(Cu), iron (Fe), mercury (Hg), lead (Pb), nickel (Ni),tin (Sri), and zinc (Zn) because of their toxicityand/or high market value (86). Military sources ofheavy metals include munitions production, metalplating, aircraft and motor vehicle washing, paint-stripping and metal-working, photographic pro-cessing and cooling water system blowdown. Themost commonly used heavy metal removal tech-niques are chemical precipitation, metallic replace-ment, electrodeposition, ion exchange, evapora-tion, and reverse osmosis, although solventextraction, activated carbon adsorption and ionflotation are being developed and are applicable insome situations (32)(33)(39)(86).

(a) Chemical precipitation. the most com-monly used removal method, particularly whenmetal recovery is not a consideration, is precipita-tion. This process is based on the fact that mostmetal hydroxides are only slightly soluble andthat some metal carbonates and sulfides are also

only sparingly water soluble. The typical precipi-tation process using sodium hydroxide or lime asa reactant is generally applicable to copper, zinc, iron or nickel removal with no special modifica-tions.

–Chromium exists in wastewater in boththe highly toxic hexavalent and theless toxic trivalent forms. To precipi-tate chromium, the hexavalent formmust first be reduced to the trivalentform using reducing agents such assulfur dioxide, ferrous sulfate, metalliciron, or sodium bisulfite. The reactionis best performed in an acidic solutionwith a pH of 2.0 to 3.0. The trivalentchromium is precipitated as chromiumhydroxide by raising the pH with limeor sodium hydroxide (34)(39)(86).

–Cadmium hydroxide precipitation bylime occurs at high pH. If cyanide isalso present (as inplating waste), itmust be eliminated first by addingsodium sulfide. The proprietary“Kastone” process is a hydrogen perox-ide oxidation-precipitation systemwhich simultaneously oxidizes and pre-cipitates cadmium as cadmium oxidewhich can be recycled to some processsolutions (130).

–Lead may be precipitated by substitut-ing soda ash for lime in the conven-tional lime precipitation scheme. Bothmercury and silver as well as lead maybe precipitated as sulfides with theaddition of combinations of sodium sul-fide, sodium thiosulfate or sodium hy-droxide (21)(86). The precipitated sul-fide sludge may be sold to a refineryfor recovery (130).

(b) Metallic replacement. The metallic re-placement or displacement process is used whenmetal recovery is desirable, such as silver recov-ery from photographic wastes and copper recov-ery from brass-working wastes. In this process, ametal which is more active than the metal to berecovered is placed into the waste solution. Themore active metal goes into solution, replacingthe less active metal which precipitates (or plates)out and is recovered. Zinc or iron, in the form ofeither dust or finely-spun wool, is often used torecover silver or copper (30)(86). A proprietaryspun-iron cartridge is used to recover silver fromwaste photographic fixing solutions in normally acontinuous operation (111). The treated fixing solution may still contain at least 1,000 mg/L ofsilver as well as the ionized iron and cannot be

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TM 5-814-8

reused because the iron is a contaminant in thefixing process. The high residual concentration ofpotentially toxic metal also requires that benchand/or pilot scale studies be used to establish thetreatability of the waste by conventional biologi-cal systems.

(c) Electrodeposition. Like metallic replace-ment, electrolytic recovery is used to recovervaluable metals such as silver or copper fromphotographic processing, brass pickling or copper-plating wastes. When a direct electrical current ofthe proper density is passed through thewastewater solution, the metal in solution platesout in a pure form on the cathode. The electro-lytic method may be operated continuously orbatch-wise, is effective over a range of 1000 to100,000 mg/L of influent metal and may producean effluent as low as 500 mg/L of metal. How-ever, close supervision is required in order tomaintain proper current density (30)(86)(130).Again, the residual metal concentrations are highenough to limit biological treatment of the waste.

(d) Ion exchange. Ion exchange technologyhas been developed for treating chromium wastesfrom plating processing to include chromiumdetoxification or recovery, water reuse and heatrecovery from hot rinses. This is normally acontinuous flow process rather than a batch-typeoperation. Mixed wastes of chromium and cya-nides can be treated first by a cation exchangerto remove metals from complex metal cyanidesgenerating hydrogen cyanide, and then by ananion exchanger to remove the liberated cyanide.The concentrated solution formed by regeneratingthe exchange resins can be a source of recoverableproduct in many cases (34). Ion exchange is alsobeing investigated for the recovery of silver fromphotographic processing wastes, chromate fromcooling water system blowdown (115) and cad-mium from plating solutions.

(e) Evaporation. Evaporation is used torecover heavy metals particularly chromate fromsome plating solutions. Evaporation by applyingheat or vacuum to the solution may be employed.The distilled water from evaporation is reused asprocess rinse water (129). Rinsing with highpurity water results in low rinse water use.

(f) Reverse osmosis and ultrafiltration. Re-verse osmosis and ultrafiltration processes havebeen rapidly improved in recent years, and areused in several cases to treat plating rinse waters.Use of membrane processes for treatment ofcooling water blowdown for dissolved solids andchromate removal has also been reported(45)(50)(92).

(3) Cyanide destruction. Cyanides are foundprincipally in metal plating wastes (includingthose wastes from metal-renovation operations)and photographic processing wastewaters. Themost toxic form of cyanide is hydrogen cyanide(HCN), while the complex iron cyanides (Fe(CN6)

-4

and (Fe(CN)6)-3 and the cyanate (CNO) - are less

toxic by several orders of magnitude. The mostwidely used cyanide destruction process is alka-line chlorination. Other treatment processes whichhave been used in actual practice include oxida-tion using hydrogen peroxide (including the pro-prietary “Kastone” process), and ion exhange(32)(33)(34).

(a) Alkaline chlorination. Alkaline chlorina-tion involves oxidation of the cyanide to carbondioxide and nitrogen gas using chlorine in a highpH solution. This is normally a single-step reac-tion requiring about 4 hours with a solution pHof 11. A two-step operation consists of cyanideconversion to cyanate at pH of 11, requiringabout 30 minutes, followed by complete destruc-tion of cyanate to carbon dioxide and nitrogengas at pH of 8, requiring another 30 minutes.About 5 mg/l of excess chlorine is maintained(129). Vigorous agitation is required, especiallywhen metal-cyanide complexes are present, toprevent precipitation of untreated cyanide salts(34)(130). Generally, flows smaller than 20,000gallons per day use batch treatment in two tanks,in which one tank of waste is treated while theother is filling. A continuous treatment schemerequires instrumentation to control the chemicaladditions, and is normally uneconomical for smallflows. Either chlorine gas or hypochlorites maybe used as the chlorine source, depending oneconomics and particular preference. Either so-dium hydroxide or lime is used to raise the pH(34)(109).

(b) Hydrogen peroxide oxidation. Cyanidesmay be oxidized to cyanate by hydrogen perox-ide. This process is used in Europe and has theadvantage of not introducing an additional pollut-ant (residual chlorine) into the water (33). Theproprietary “Kastone” process is basically a hy-drogen peroxide-formaldehyde method of cyanideoxidation. Formaldehyde reacts with the cyanideto form formaldo-cyanohydrin which is readilyoxidized by the hydrogen peroxide. This processis particularly advantageous for plating wastetreatment because the hydrogen peroxide alsoprecipitates bevy metals as oxides (124).

(c) Ion exchange. Ion exchange using astrong base anion exchange resin can removecyanides effectively from plating wastes, althoughnot always from photographic wastes due to resin

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TM 5-814-8

poisoning by the iron cyanide complexes.Wastewater is first passed through a cationexchanger to remove metals, breakup complexmetal cyanides, and free the cyanide for removalby the successive anion exchanger. The anionresin may be regenerated with caustic, recover-ing the cyanide as sodium cyanide. The volume ofthe recovered cyanide solution is only 10 to 20p e r c e n t o f t h e o r i g i n a l w a s t e v o l u m e(34)(109)(111).

(4) Oil removal. Wastewater from munitionsmetal parts manufacturing and flows from air-craft and vehicle washing, paint-stripping andmetal-working operations may contain large quan-tities of oils in any of three forms: free floatingoil, emulsified oil or soluble oil. Physical, chemicaland biological treatment steps may be used invarious combinations in order to reduce oil con-centrations to levels required by water usage orregulatory criteria.

(a) Free oils. Free oils readily float to thewater surface to be removed by gravity separa-tors such as conventional primary clarifiers withsurface skimming devices or separators designedaccording to American Petroleum Institute (API)criteria. The effectiveness of these and othermeans of removing free oil from wastewatervaries depending on the type of oil, temperatureof the waste, and other factors. As a guide,however, some generalizations can be made. Grav-ity separation devices are effective in reducing oilconcentrations to about 150 to 200 mg/L. Dis-solved air flotation, similar to that used tothicken sludge, is effective in reducing oil levelsto 50 to 100 mg/L. Granular media filters, pre-ceded by gravity or flotation separators, canreduce oil concentrations to 10 to 20 mg/L.Chemical coagulation and precipitation, followedby gravity separation or dissolved air flotation,can remove all but about 5 mg/L of oil(95)(129)(156).

(b) Emulsified oils. Emulsions can be eitheroil-in-water or water-in-oil types. The more com-mon oil-in-water emulsions are dispersions of tinydroplets or oil suspended in water. Emulsifyingagents such as soaps, sulfated oils and alcoholsand various fine particles enhance the stability ofthe dispersed oil, preventing the droplets frommerging together into larger droplets which couldbe removed from the water (95). Prepared emul-sions are used as coolants and lubricants inmachining operations. Emulsions are also formedwhen oily wastewater comes in contact withsteam, soaps, caustic or agitation. The emulsionmust first be broken, then the oil released isremoved as a free oil. Emulsion cracking is the

term used to describe treatment of wastewatercontaining large amounts (2 to 7 percent) ofemulsified oils, such as emulsions used in machin-ing operations. Cracking involves addition of chemicals such as sulfuric acid, iron salts, alum,calcium chloride, or proprietary organic com-pounds, followed by heating to 100 to 140 degreesF. This is followed by two to four hours ofcoalescence. The effluent may still contain a fewhundred mg/L of emulsified oil, and should befurther treated, along with other waste streamshaving a similar level of oil content, by addingcoagulating salts to lower the oil concentration.Wastewaters with less than 500 to 1000 mg/L ofemulsified oil, or the effluent from the crackingstep, may be treated by adding iron or aluminumsulfate salts, forming a metal hydroxide-oil sludge(95)(108)(129). A typical treatment scheme isshown on figure 6-2.

(c) Soluble oils. Soluble oils, such as certainanimal and vegetable oils, may be readily re-moved by conventional biological treatment pro-cesses (89)( 120). In general, oils derived frompetroleum are neither readily soluble norbiodegradable, although biological systems canbe developed to provide treatment of some of thesoluble fractions of petroleum oils. Domestic sew-age helps to provide inorganic nutrients essentialfor the biological degradation of the high BODoils.

(5) Deep well injection. Pumping waste liq-uids into deep wells which tap porous rockformations has been used to dispose of “untreat-able” or hard-to-treat organic and inorganicwastes from various industries.

(a) Pretreatment requirements. Wastesmust be pretreated to remove any suspendedsolids which could clog the pores of the receivingrock formation. In addition, biological growth(and the resultant slime formation or corrosion)must be inhibited with the addition of biocides.Typical pre-injection treatment is costly and in-cludes chemical addition, neutralization, oil re-moval, clarification and multi-stage filtration.

(b) Geological requirements. Careful geol-ogy and soils investigations must be undertakento find a deep strata which is confined so thatwaste fluids will never reach a fresh water aquifer(92). The underground disposal area must alsohave satisfactory reservoir storage (107). Thewaste must not be capable of reaction with thebrine at disposal level to form an insolublematerial. Extreme care must be taken in drilling,constructing, and sealing the well to prevent anycontamination of groundwater in other subterra- nean formations (37). Well casings must be highly

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TM 5-814-8

MACHINING FLUIDS(2 TO 7% OIL)

I

CHEMICALADDITION

- iRAPID MIX I

ACID ‘NEUTRALIZATION

(If Required)

Figure 6-2. Emulsified oil removal by cracking and chemical coagulation.

corrosion-resistant to prevent leakage from corro-sion caused by high pressure injection of acidsand salts. Duplicate wells should be drilled ifthere is no alternative treatment or holdingcapacity in case the disposal well should fail. Inaddition, a number of sample wells must bedrilled and maintained in order to monitor any

--- leakage into ground water (72)(107). Trace leakagemay be impossible to identify.

(c) Application to military wastes. Due tothe extreme need for providing a fail-safe system,deep well injection is an expensive undertaking.Because of uncertainties with deep well opera-tions (well leaks or clogging), careful comparisonshould be made of all other possible treatmentalternatives prior to initiating a deep well system.Present U.S. EPA and Army policies discouragedeep well disposal. The U.S. EPA requires proof

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TM 5-814-8

that no adverse environmental impacts will result expensive, research effort. In general, deep wellfrom construction or operation of the well injection is an unacceptable process for handling(99)(102). This can often require involved, and military installation wastewaters.

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